Revenue Recognition - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings	$ (75,554)		$ (75,554)			$ (71,453)
Deferred revenue	700		700
Deferred expense	200		200		$ 400
Operating expenses	(43,577)	$ (37,250)	(87,958)	$ (81,417)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to retained earnings					300
Deferred revenue					$ 700
Operating expenses	$ (3,078)		$ (6,624)