Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Property and equipment	$ 1,942	$ 473
Stock-based compensation	22,050	23,071
Reserves and accruals not currently deductible	41,024	49,436
Net operating losses	2,432	1,140
Tax credits	30,831	15,015
Other	2,115	194
Gross deferred tax assets	100,394	89,329
Valuation allowance	(35,132)	(16,894)
Total deferred tax assets	65,262	72,435
Deferred tax liabilities:
Property and equipment	0	(198)
Accrued liabilities	(2,006)	(2,555)
Other	(9)	(3)
Total deferred tax liabilities	(2,015)	(2,756)
Net deferred tax assets	63,247	69,679
Deferred Tax Assets, Net of Valuation Allowance, Classification [Abstract]
Deferred tax assets, non-current	65,125	70,960
Deferred tax liabilities, non-current	$ (1,878)	$ (1,281)