Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Federal statutory income tax rate		34.00%
Claim settlement received	$ 14,500,000		$ 14,452,000
Settlement recognized as additional paid-in capital, net of tax			9,495,000
Income tax benefit, claims settlement			5,000,000
Increase in deferred tax assets valuation allowance		$ 23,800,000	$ 5,000,000	$ 9,800,000
Deferred tax assets, net operating loss carryforwards for federal		412,000,000
Deferred tax assets, net operating loss carryforwards for state		177,000,000
Federal research tax credit carryforwards		9,700,000
State research tax credit carryforwards		$ 10,500,000
Tax credit carryforward, expiration year		2018
Accrued interest and/or penalties		$ 0
State
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2018
Federal
Income Taxes [Line Items]
Operating loss carryforwards, expiration year		2018