Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 21,527
Income before taxes
Domestic		$ 46,031	$ 38,211	$ 58,498
Foreign		(5,042)	(15,574)	1,733
Income before income taxes		40,989	22,637	60,231
Federal:
Current		20,661	22,115	20,497
Deferred		43,678	(2,198)	(170,798)
State:
Current		495	884	609
Deferred		(43)	(271)	(1,933)
Foreign:
Current		1,101	1,275	443
Deferred		(2,041)	(5,988)	25
Provision for (benefit from) income taxes		$ 63,851	$ 15,817	$ (151,157)
Effective income tax rate reconciliation
Expense (benefit) at U.S. federal statutory rate (as a percent)		35.00%	35.00%	35.00%
Expense (benefit) at state statutory rate (as a percent)		0.70%	1.80%	(1.50%)
Withholding tax (as a percent)		50.10%	97.00%	34.10%
Foreign rate differential (as a percent)		2.80%	4.10%	0.40%
Research and development ("R&D") credit (as a percent)		(3.90%)	(8.30%)	(2.30%)
Executive compensation (as a percent)		1.80%	1.50%	0.50%
Non-deductible stock-based compensation (as a percent)		14.90%	34.80%	5.30%
Foreign tax credit (as a percent)		(50.10%)	(97.00%)	(34.10%)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent		50.60%	0.00%	0.00%
Other (as a percent)		1.40%	1.00%	(0.60%)
Valuation allowance (as a percent)		52.50%	0.00%	(287.80%)
Effective tax rate (as a percent)		155.80%	69.90%	(251.00%)
Components of net deferred tax assets
Depreciation and amortization	10,840	$ 10,840	$ 22,348
Other liabilities and reserves	8,766	8,766	12,268
Deferred equity compensation	7,979	7,979	17,426
Net operating loss carryovers	16,335	16,335	11,439
Tax credits	157,051	157,051	120,660
Total gross deferred tax assets	200,971	200,971	184,141
Convertible debt	(791)	(791)	(3,870)
Total net deferred tax assets	200,180	200,180	180,271
Valuation allowance	(50,911)	(50,911)	(23,529)
Net deferred tax assets	149,269	149,269	156,742
Net deferred tax assets reported as:
Non-current deferred tax assets	159,099	159,099	168,342
Non-current deferred tax liabilities	(9,830)	(9,830)	(11,600)
Net deferred tax assets	$ 149,269	$ 149,269	$ 156,742