Annual report pursuant to Section 13 and 15(d)

Recent Accounting Pronouncements - Narrative (Details)

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Recent Accounting Pronouncements - Narrative (Details) - USD ($)
$ in Thousands
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Capitalized Contract Cost [Line Items]        
Expected cumulative adjustment, reduction to opening retained earnings   $ 334,219 $ 222,924  
Difference between Revenue Guidance in Effect before and after Topic 606 | Subsequent Event | Accounting Standards Update 2014-09 | Minimum        
Capitalized Contract Cost [Line Items]        
Expected cumulative adjustment, reduction to opening retained earnings $ 25,000      
Difference between Revenue Guidance in Effect before and after Topic 606 | Subsequent Event | Accounting Standards Update 2014-09 | Maximum        
Capitalized Contract Cost [Line Items]        
Expected cumulative adjustment, reduction to opening retained earnings $ 35,000      
Moves Costs        
Capitalized Contract Cost [Line Items]        
Capitalized costs   $ 15,075 $ 15,021 $ 13,086