Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Revenue Recognition (Details)

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Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Jan. 01, 2018
Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Increase (decrease) in retained earnings $ 238,378   $ 231,390 $ 235,844
Decrease in revenues (167,410) $ (134,610)    
Effect of Change Higher/(Lower) | Accounting Standards Update 2014-09        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Increase (decrease) in retained earnings (3,345)   $ (4,454)  
Decrease in revenues $ 829