Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Line Items]
Federal income tax expense (benefit)	$ 0	$ 0	$ 0
State income tax expense (benefit)	$ 0	0	$ 0
Net operating loss and tax credit carryforwards ownership interest changing period	3 years
Ownership interest rate of net operating loss and tax credit carryforwards	50.00%
Net operating loss carryforwards, limitation on use	$ 1,500,000
Uncertain tax positions	0	$ 0
Accrued interest or penalties related to uncertain tax positions	0
Increase in the valuation allowance	41,500,000
Federal Tax Authority [Member]
Income Tax [Line Items]
Net operating loss carryforwards	267,500,000
Federal net operating loss carryforwards, deductions	$ 38,900,000
Expiration of net operating loss carryforwards	2029
Tax credit carryforwards	$ 8,700,000
Expiration of tax credit carryforwards	2029
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Net operating loss carryforwards	$ 227,500,000
Federal net operating loss carryforwards, deductions	$ 31,700,000
Expiration of net operating loss carryforwards	2019
Tax credit carryforwards	$ 5,800,000
Expiration of tax credit carryforwards	2017