Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax Credit Carryforward
Deferred tax assets, valuation allowance	$ 17,111	$ 9,998
Unrecognized tax benefits	9,029	6,586	$ 5,703	$ 8,566
Reductions for tax positions of prior years	0	$ 68	$ 3,913
Unrecognized tax benefits that would decrease effective tax rate in period	4,500
Federal
Tax Credit Carryforward
Net operating loss carryforwards	700
Federal | Research Tax Credit Carryforward
Tax Credit Carryforward
Tax credit carryforwards	$ 12,500
Tax credits carryforward period	20 years
State and Local Jurisdiction | Research Tax Credit Carryforward
Tax Credit Carryforward
Tax credit carryforwards	$ 16,500
California
Tax Credit Carryforward
Net operating loss carryforwards	$ 23,500
Arizona | Research Tax Credit Carryforward
Tax Credit Carryforward
Tax credits carryforward period	15 years