CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Balance Sheets) (Details) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Dec. 31, 2016 |
Current assets: |
|
|
|
|
Cash and cash equivalents |
$ 124,571
|
$ 99,557
|
|
|
Accounts receivable - oil and natural gas sales |
157,391
|
146,773
|
|
|
Accounts receivable - joint interest and other |
39,511
|
35,440
|
|
|
Accounts receivable - related parties |
79
|
0
|
|
|
Accounts receivable - intercompany |
0
|
0
|
|
|
Prepaid expenses and other current assets |
9,742
|
4,912
|
|
|
Short-term derivative instruments |
19,809
|
78,847
|
|
|
Total current assets |
351,103
|
365,529
|
|
|
Property and equipment: |
|
|
|
|
Oil and natural gas properties |
9,936,714
|
9,169,156
|
|
|
Other property and equipment |
92,388
|
86,754
|
|
|
Accumulated depletion, depreciation, amortization and impairment |
(4,506,306)
|
(4,153,733)
|
|
|
Property and equipment, net |
5,522,796
|
5,102,177
|
|
|
Other assets: |
|
|
|
|
Equity investments and investments in subsidiaries |
232,529
|
302,112
|
|
|
Long-term derivative instruments |
3,530
|
8,685
|
|
|
Deferred tax asset |
0
|
1,208
|
|
|
Inventories |
8,234
|
8,227
|
|
|
Other assets |
17,038
|
19,814
|
|
|
Total other assets |
261,331
|
340,046
|
|
|
Total assets |
6,135,230
|
5,807,752
|
|
|
Current liabilities: |
|
|
|
|
Accounts payable and accrued liabilities |
582,464
|
553,609
|
|
|
Accounts payable - intercompany |
0
|
0
|
|
|
Asset retirement obligation—current |
120
|
120
|
$ 195
|
|
Short-term derivative instruments |
62,601
|
32,534
|
|
|
Current maturities of long-term debt |
647
|
622
|
|
|
Total current liabilities |
645,832
|
586,885
|
|
|
Long-term derivative instruments |
15,101
|
2,989
|
|
|
Asset retirement obligation—long-term |
78,411
|
74,980
|
44,266
|
|
Deferred tax liability |
3,046
|
0
|
|
|
Other non-current liabilities |
0
|
2,963
|
|
|
Long-term debt, net of current maturities |
2,100,825
|
2,038,321
|
|
|
Total liabilities |
2,843,215
|
2,706,138
|
|
|
Stockholders’ equity: |
|
|
|
|
Common stock |
1,732
|
1,831
|
|
|
Paid-in capital |
4,316,006
|
4,416,250
|
|
|
Accumulated other comprehensive (loss) income |
(46,354)
|
(40,539)
|
|
|
Retained (deficit) earnings |
(979,369)
|
(1,275,928)
|
|
|
Total stockholders’ equity |
3,292,015
|
3,101,614
|
$ 2,942,661
|
$ 2,183,892
|
Total liabilities and stockholders’ equity |
6,135,230
|
5,807,752
|
|
|
Reportable legal entities | Parent |
|
|
|
|
Current assets: |
|
|
|
|
Cash and cash equivalents |
89,214
|
67,908
|
|
|
Accounts receivable - oil and natural gas sales |
111,463
|
112,686
|
|
|
Accounts receivable - joint interest and other |
19,066
|
15,435
|
|
|
Accounts receivable - related parties |
79
|
|
|
|
Accounts receivable - intercompany |
662,319
|
554,439
|
|
|
Prepaid expenses and other current assets |
7,521
|
4,719
|
|
|
Short-term derivative instruments |
19,809
|
78,847
|
|
|
Total current assets |
909,471
|
834,034
|
|
|
Property and equipment: |
|
|
|
|
Oil and natural gas properties |
7,003,396
|
6,562,147
|
|
|
Other property and equipment |
91,637
|
86,711
|
|
|
Accumulated depletion, depreciation, amortization and impairment |
(4,506,267)
|
(4,153,696)
|
|
|
Property and equipment, net |
2,588,766
|
2,495,162
|
|
|
Other assets: |
|
|
|
|
Equity investments and investments in subsidiaries |
2,723,140
|
2,361,575
|
|
|
Long-term derivative instruments |
3,530
|
8,685
|
|
|
Deferred tax asset |
|
1,208
|
|
|
Inventories |
6,800
|
5,816
|
|
|
Other assets |
13,018
|
12,483
|
|
|
Total other assets |
2,746,488
|
2,389,767
|
|
|
Total assets |
6,244,725
|
5,718,963
|
|
|
Current liabilities: |
|
|
|
|
Accounts payable and accrued liabilities |
464,426
|
416,249
|
|
|
Accounts payable - intercompany |
240,310
|
63,373
|
|
|
Asset retirement obligation—current |
120
|
120
|
|
|
Short-term derivative instruments |
62,601
|
32,534
|
|
|
Current maturities of long-term debt |
647
|
622
|
|
|
Total current liabilities |
768,104
|
512,898
|
|
|
Long-term derivative instruments |
15,101
|
2,989
|
|
|
Asset retirement obligation—long-term |
65,634
|
63,141
|
|
|
Deferred tax liability |
3,046
|
|
|
|
Other non-current liabilities |
|
0
|
|
|
Long-term debt, net of current maturities |
2,100,825
|
2,038,321
|
|
|
Total liabilities |
2,952,710
|
2,617,349
|
|
|
Stockholders’ equity: |
|
|
|
|
Common stock |
1,732
|
1,831
|
|
|
Paid-in capital |
4,316,006
|
4,416,250
|
|
|
Accumulated other comprehensive (loss) income |
(46,354)
|
(40,539)
|
|
|
Retained (deficit) earnings |
(979,369)
|
(1,275,928)
|
|
|
Total stockholders’ equity |
3,292,015
|
3,101,614
|
|
|
Total liabilities and stockholders’ equity |
6,244,725
|
5,718,963
|
|
|
Reportable legal entities | Guarantors |
|
|
|
|
Current assets: |
|
|
|
|
Cash and cash equivalents |
35,357
|
31,649
|
|
|
Accounts receivable - oil and natural gas sales |
45,928
|
34,087
|
|
|
Accounts receivable - joint interest and other |
20,445
|
20,005
|
|
|
Accounts receivable - related parties |
0
|
|
|
|
Accounts receivable - intercompany |
240,373
|
63,374
|
|
|
Prepaid expenses and other current assets |
2,221
|
193
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Total current assets |
344,324
|
149,308
|
|
|
Property and equipment: |
|
|
|
|
Oil and natural gas properties |
2,934,047
|
2,607,738
|
|
|
Other property and equipment |
751
|
43
|
|
|
Accumulated depletion, depreciation, amortization and impairment |
(39)
|
(37)
|
|
|
Property and equipment, net |
2,934,759
|
2,607,744
|
|
|
Other assets: |
|
|
|
|
Equity investments and investments in subsidiaries |
|
77,744
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Deferred tax asset |
|
0
|
|
|
Inventories |
1,434
|
2,411
|
|
|
Other assets |
4,020
|
7,331
|
|
|
Total other assets |
5,454
|
87,486
|
|
|
Total assets |
3,284,537
|
2,844,538
|
|
|
Current liabilities: |
|
|
|
|
Accounts payable and accrued liabilities |
118,038
|
137,361
|
|
|
Accounts payable - intercompany |
662,254
|
554,313
|
|
|
Asset retirement obligation—current |
0
|
0
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Current maturities of long-term debt |
0
|
0
|
|
|
Total current liabilities |
780,292
|
691,674
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Asset retirement obligation—long-term |
12,777
|
11,839
|
|
|
Deferred tax liability |
0
|
|
|
|
Other non-current liabilities |
|
2,963
|
|
|
Long-term debt, net of current maturities |
0
|
0
|
|
|
Total liabilities |
793,069
|
706,476
|
|
|
Stockholders’ equity: |
|
|
|
|
Common stock |
0
|
0
|
|
|
Paid-in capital |
1,915,598
|
1,915,598
|
|
|
Accumulated other comprehensive (loss) income |
0
|
0
|
|
|
Retained (deficit) earnings |
575,870
|
222,464
|
|
|
Total stockholders’ equity |
2,491,468
|
2,138,062
|
|
|
Total liabilities and stockholders’ equity |
3,284,537
|
2,844,538
|
|
|
Reportable legal entities | Non-Guarantor |
|
|
|
|
Current assets: |
|
|
|
|
Cash and cash equivalents |
0
|
0
|
|
|
Accounts receivable - oil and natural gas sales |
0
|
0
|
|
|
Accounts receivable - joint interest and other |
0
|
0
|
|
|
Accounts receivable - related parties |
0
|
|
|
|
Accounts receivable - intercompany |
0
|
0
|
|
|
Prepaid expenses and other current assets |
0
|
0
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Total current assets |
0
|
0
|
|
|
Property and equipment: |
|
|
|
|
Oil and natural gas properties |
0
|
0
|
|
|
Other property and equipment |
0
|
0
|
|
|
Accumulated depletion, depreciation, amortization and impairment |
0
|
0
|
|
|
Property and equipment, net |
0
|
0
|
|
|
Other assets: |
|
|
|
|
Equity investments and investments in subsidiaries |
53,380
|
57,641
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Deferred tax asset |
|
0
|
|
|
Inventories |
0
|
0
|
|
|
Other assets |
0
|
0
|
|
|
Total other assets |
53,380
|
57,641
|
|
|
Total assets |
53,380
|
57,641
|
|
|
Current liabilities: |
|
|
|
|
Accounts payable and accrued liabilities |
0
|
0
|
|
|
Accounts payable - intercompany |
128
|
127
|
|
|
Asset retirement obligation—current |
0
|
0
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Current maturities of long-term debt |
0
|
0
|
|
|
Total current liabilities |
128
|
127
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Asset retirement obligation—long-term |
0
|
0
|
|
|
Deferred tax liability |
0
|
|
|
|
Other non-current liabilities |
|
0
|
|
|
Long-term debt, net of current maturities |
0
|
0
|
|
|
Total liabilities |
128
|
127
|
|
|
Stockholders’ equity: |
|
|
|
|
Common stock |
0
|
0
|
|
|
Paid-in capital |
261,626
|
259,307
|
|
|
Accumulated other comprehensive (loss) income |
(44,338)
|
(38,593)
|
|
|
Retained (deficit) earnings |
(164,036)
|
(163,200)
|
|
|
Total stockholders’ equity |
53,252
|
57,514
|
|
|
Total liabilities and stockholders’ equity |
53,380
|
57,641
|
|
|
Eliminations |
|
|
|
|
Current assets: |
|
|
|
|
Cash and cash equivalents |
0
|
0
|
|
|
Accounts receivable - oil and natural gas sales |
0
|
0
|
|
|
Accounts receivable - joint interest and other |
0
|
0
|
|
|
Accounts receivable - related parties |
0
|
|
|
|
Accounts receivable - intercompany |
(902,692)
|
(617,813)
|
|
|
Prepaid expenses and other current assets |
0
|
0
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Total current assets |
(902,692)
|
(617,813)
|
|
|
Property and equipment: |
|
|
|
|
Oil and natural gas properties |
(729)
|
(729)
|
|
|
Other property and equipment |
0
|
0
|
|
|
Accumulated depletion, depreciation, amortization and impairment |
0
|
0
|
|
|
Property and equipment, net |
(729)
|
(729)
|
|
|
Other assets: |
|
|
|
|
Equity investments and investments in subsidiaries |
(2,543,991)
|
(2,194,848)
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Deferred tax asset |
|
0
|
|
|
Inventories |
0
|
0
|
|
|
Other assets |
0
|
0
|
|
|
Total other assets |
(2,543,991)
|
(2,194,848)
|
|
|
Total assets |
(3,447,412)
|
(2,813,390)
|
|
|
Current liabilities: |
|
|
|
|
Accounts payable and accrued liabilities |
0
|
(1)
|
|
|
Accounts payable - intercompany |
(902,692)
|
(617,813)
|
|
|
Asset retirement obligation—current |
0
|
0
|
|
|
Short-term derivative instruments |
0
|
0
|
|
|
Current maturities of long-term debt |
0
|
0
|
|
|
Total current liabilities |
(902,692)
|
(617,814)
|
|
|
Long-term derivative instruments |
0
|
0
|
|
|
Asset retirement obligation—long-term |
0
|
0
|
|
|
Deferred tax liability |
0
|
|
|
|
Other non-current liabilities |
|
0
|
|
|
Long-term debt, net of current maturities |
0
|
0
|
|
|
Total liabilities |
(902,692)
|
(617,814)
|
|
|
Stockholders’ equity: |
|
|
|
|
Common stock |
0
|
0
|
|
|
Paid-in capital |
(2,177,224)
|
(2,174,905)
|
|
|
Accumulated other comprehensive (loss) income |
44,338
|
38,593
|
|
|
Retained (deficit) earnings |
(411,834)
|
(59,264)
|
|
|
Total stockholders’ equity |
(2,544,720)
|
(2,195,576)
|
|
|
Total liabilities and stockholders’ equity |
$ (3,447,412)
|
$ (2,813,390)
|
|
|