Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 37,417	$ 26,926
Tax credit carryforwards	12,751	8,432
Deferred revenue	26,739	31,735
Deferred lease incentive	103	120
Deferred rent	476	431
Intangibles	552	237
Accrued expenses and other	1,091	995
Unrealized loss on available-for-sale securities	39	112
Stock-based compensation	2,119	713
Total deferred tax assets	81,287	69,701
Less: valuation allowance	(55,348)	(30,850)
Net deferred tax assets	25,939	38,851
Deferred tax liabilities:
Section 481(a) method change	(25,653)	(38,481)
Depreciation	(286)	(370)
Total deferred tax liabilities	(25,939)	(38,851)
Net deferred taxes	$ 0	$ 0