Available-for-Sale Marketable Securities in Unrealized Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 36,118	$ 40,121
Less than 12 Months, Unrealized Loss	(28)	(24)
Total, Fair Value	36,118	40,121
Total, Unrealized Loss	(28)	(24)
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	18,088	6,035
Less than 12 Months, Unrealized Loss	(18)	(1)
Total, Fair Value	18,088	6,035
Total, Unrealized Loss	(18)	(1)
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	18,030	34,086
Less than 12 Months, Unrealized Loss	(10)	(23)
Total, Fair Value	18,030	34,086
Total, Unrealized Loss	$ (10)	$ (23)