Annual report pursuant to Section 13 and 15(d)

Fair Value of Financial Instruments (Details)

v3.8.0.1
Fair Value of Financial Instruments (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Deferred finance costs $ 34,781 $ 27,174
Senior notes | 6.625% Senior Notes Due 2023    
Debt Instrument [Line Items]    
Deferred finance costs 5,200  
Senior notes | 6.000% Senior Notes Due 2024    
Debt Instrument [Line Items]    
Deferred finance costs 9,900  
Senior notes | 6.375% Senior Notes Due 2025    
Debt Instrument [Line Items]    
Deferred finance costs 14,000  
Senior notes | 6.375% Senior Notes Due 2026    
Debt Instrument [Line Items]    
Deferred finance costs 5,500  
Carrying value | Senior notes    
Debt Instrument [Line Items]    
Fair value of notes 2,000,000  
Fair value | Senior notes    
Debt Instrument [Line Items]    
Fair value of notes $ 2,100,000