Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Examination [Line Items]
Income tax provision	$ (223,000)	$ (1,839,000)	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ (2,062,000)	$ 0	$ 0
Federal taxes									1,800,000
State taxes									200,000
Deferred tax assets attributable to excess stock option benefits	10,256,000				$ 12,683,000				10,256,000	$ 12,683,000
Increase (decrease) in net valuation allowance of deferred tax asset									39,500,000
Unrecognized tax benefits, interest and penalties									0
Options to purchase common stock
Income Tax Examination [Line Items]
Deferred tax assets attributable to excess stock option benefits	6,800,000								6,800,000
Internal Revenue Service (IRS)
Income Tax Examination [Line Items]
Net operating losses	594,900,000								594,900,000
Internal Revenue Service (IRS) | Research Tax Credit Carryforward
Income Tax Examination [Line Items]
Research and development tax credit carryforwards	6,200,000								$ 6,200,000
Internal Revenue Service (IRS) | Minimum
Income Tax Examination [Line Items]
Net operating loss carryforwards, expiry date									2024
Internal Revenue Service (IRS) | Minimum | Research Tax Credit Carryforward
Income Tax Examination [Line Items]
Research and development tax credits, expiry date									2028
State and Local Jurisdiction
Income Tax Examination [Line Items]
Net operating losses	364,500,000								$ 364,500,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Income Tax Examination [Line Items]
Research and development tax credit carryforwards	4,100,000								$ 4,100,000
State and Local Jurisdiction | Minimum
Income Tax Examination [Line Items]
Net operating loss carryforwards, expiry date									2017
Foreign Tax Authority
Income Tax Examination [Line Items]
Net operating losses	$ 14,500,000								$ 14,500,000