Subsequent Event - Additional Information (Detail) - Subsequent Event [Member] $ in Millions		1 Months Ended	3 Months Ended
	Oct. 06, 2017 Employee	Oct. 31, 2017 shares	Dec. 31, 2017 USD ($)
Restructuring Plan [Member]
Subsequent Event [Line Items]
Restructuring plan effective date		Oct. 20, 2017
Number of employees to be reduced | Employee	45
Approximate reduction as a percent of workforce	62.00%
Restructuring plan notification date to affected employees		Oct. 06, 2017
Restructuring Plan [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
One-time severance-related charge | $			$ 3.4
Severance Benefit Plan [Member]
Subsequent Event [Line Items]
Vesting period of shares granted to retained employees		2 years
Cash retention bonus percentage of each retained employees then current base salary		50.00%
Required additional continuing employment period for retained employees		12 months
Severance Benefit Plan [Member] | Restricted stock units [Member]
Subsequent Event [Line Items]
Approximate number of shares granted to retained employees | shares		907,000