Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Financial Instruments (Narrative) (Details)

v3.8.0.1
Fair Value of Financial Instruments (Narrative) (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Unamortized debt issuance costs $ 33,927 $ 34,781
Senior notes | 6.625% Senior Notes due 2023    
Debt Instrument [Line Items]    
Unamortized debt issuance costs 5,000  
Senior notes | 6.000% Senior Notes due 2024    
Debt Instrument [Line Items]    
Unamortized debt issuance costs 9,600  
Senior notes | 6.375% Senior Notes due 2025    
Debt Instrument [Line Items]    
Unamortized debt issuance costs 13,600  
Senior notes | 6.375% Senior Notes Due 2026    
Debt Instrument [Line Items]    
Unamortized debt issuance costs 5,500  
Carry value | Senior notes    
Debt Instrument [Line Items]    
Carrying value of notes 2,000,000  
Fair value | Senior notes    
Debt Instrument [Line Items]    
Carrying value of notes $ 2,000,000