Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Income Taxes Disclosure [Line Items]
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions		$ 631	$ 951	$ 773
Deferred Tax Assets, Valuation Allowance	$ 7,774		15,204	7,774
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(7,400)
Unrecognized Tax Benefits	8,604	7,684	9,565	8,604	$ 7,065
Federal Net Operating Loss carryforwards			13,000
State Net Operating Loss carryforwards			23,300
Federal alternative minimum tax credit			600
Gross research credits		$ 722	$ 484	979
Cumulative changes in ownership percentage			50.00%
Cumulative changes in ownership period			3 years
Realized upon settlement			50.00%
Unrecognized tax benefits that would impact effective tax rate	6,400		$ 8,100	6,400
Accrued interest and penalties associated with uncertain tax positions	200		300	200
Interest expense, net of accrued interest reversed			0	$ 100
Federal research credits [Member]
Income Taxes Disclosure [Line Items]
Federal research credits			$ 4,300
Federal research credits, expiration date			Dec. 31, 2031
Gross State Research Credits [Member]
Income Taxes Disclosure [Line Items]
Gross research credits			$ 9,800
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount			9,500
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount			$ 300
Federal [Member]
Income Taxes Disclosure [Line Items]
Gross research credits	$ 1,000