Summary of Significant Accounting Policies - Additional Information (Detail) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Cash equivalents, highly-liquid investments maturity (or less)		3 months
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Early Exercise of Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued upon early exercise of stock options and are subject to future vesting		11,512	24,444
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Property and equipment, estimated useful lives		3 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Property and equipment, estimated useful lives		5 years