Annual report pursuant to Section 13 and 15(d)

Acquisitions - Narrative (Details)

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Acquisitions - Narrative (Details)
$ / shares in Units, shares in Millions
 2 Months Ended 12 Months Ended
Feb. 17, 2017
USD ($)
a
$ / shares
shares
Feb. 16, 2017
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 15, 2016
$ / shares
Business Acquisition [Line Items]            
Acquisition costs     $ 2,392,000 $ 0 $ 0  
Common stock share price (usd per share) | $ / shares $ 19.48         $ 20.96
Vitruvian            
Business Acquisition [Line Items]            
Net surface area acquired (in acres) | a 46,400          
Total initial price $ 1,850,000,000          
Payments to acquire businesses $ 1,354,093,000          
Equity interest issued or issuable, number of shares (in shares) | shares 23.9          
Acquisition costs     $ 2,400,000      
Goodwill $ 0          
Bargain purchase gain $ 0          
Initial purchase share price (usd per share) | $ / shares           $ 20.96
Decrease in fair value of shares issued for acquisition, amount   $ 35,300,000        
Indemnity Escrow | Vitruvian            
Business Acquisition [Line Items]            
Equity interest issued or issuable, number of shares (in shares) | shares 5.2