Income Taxes - Components of Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation
U.S. Federal tax benefit at statutory rates									$ (20,260)	$ (22,310)	$ (28,681)
State income taxes, net of federal tax benefit									(806)	(855)	(1,632)
Foreign rate differential									5,220	3,711	3,964
Stock based compensation									3,182	4,467	4,673
Other permanent differences									(494)	(750)	(99)
Deferred adjustments / U.S. rate change									7,811	0	0
Other									262	1,494	536
Valuation allowance									6,831	15,450	22,420
Total income tax provision (benefit)	$ 308	$ 503	$ 364	$ 571	$ 313	$ 218	$ 141	$ 535	$ 1,746	$ 1,207	$ 1,181