Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$ 36,825	$ 25,776	$ 19,815
Decreases recorded as benefit to income tax provision	0	0	0
Increases recorded to income tax provision	15,144	11,049	5,961
Valuation allowance as of end of year	$ 51,969	$ 36,825	$ 25,776