Summary of Significant Accounting Policies - Balance sheet as adjusted (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 420,276	$ 324,189
Deferred tax assets	47,435	49,334
Other assets	25,464	43,893
Accrued liabilities	219,035	195,562
Deferred revenues	356,109	267,713
Retained earnings	$ 328,432	267,274
As Previously Reported | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net		322,825
Deferred tax assets		50,059
Other assets		38,379
Accrued liabilities		194,198
Deferred revenues		266,842
Retained earnings		263,356
Adjustment | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net		1,364
Deferred tax assets		(725)
Other assets		5,514
Accrued liabilities		1,364
Deferred revenues		871
Retained earnings		$ 3,918