Income Taxes - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Valuation allowance		$ 131,042	$ 86,021
Increase (decrease) in valuation allowance due to deferred tax assets		(45,000)	800
Research and development tax credits		21,618	14,255
Unrecognized tax benefits, if recognized, would affect the effective tax rate		200	$ 200	$ 700
Benefits from share compensation				$ 2,700
Accounting Standards Update 2016-09 [Member]
Income Taxes [Line Items]
Increase (decrease) in valuation allowance due to deferred tax assets	$ 2,700
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 452,000
Net operating loss carryforwards expiration year		2018
Research and development tax credits		$ 15,200
Research and development tax credits beginning expiration year		2027
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 241,600
Research and development tax credits		8,200
Foreign [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 4,500
Net operating loss carryforwards expiration year		2022