Available-for-Sale Marketable Securities - Summary of Available-for-Sale Marketable Securities by Major Type of Security (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 65,974	$ 91,675
Gross Unrealized Gains	28	5
Gross Unrealized Losses	(8)	(40)
Estimated Fair Value	65,994	91,640
Money Market Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,858	42,017
Gross Unrealized Gains	19
Gross Unrealized Losses		(31)
Estimated Fair Value	18,877	41,986
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,501	2,528
Gross Unrealized Gains	1
Estimated Fair Value	2,502	2,528
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,886	13,492
Gross Unrealized Gains	4	4
Estimated Fair Value	8,890	13,496
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,054	14,194
Gross Unrealized Gains	2
Gross Unrealized Losses	(5)	(6)
Estimated Fair Value	15,051	14,188
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,675	19,444
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(3)	(3)
Estimated Fair Value	$ 20,674	$ 19,442