Short-Term Investments - Summary of Short-Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 26,656	$ 31,845
Gross Unrealized Gains	0	19
Gross Unrealized Losses	(52)	(17)
Total short-term investments, Estimated Fair Value	26,604	31,847
State, municipal and local government agencies bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		13,946
Gross Unrealized Gains		16
Gross Unrealized Losses		(1)
Total short-term investments, Estimated Fair Value		13,961
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	25,557	17,899
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(52)	(16)
Total short-term investments, Estimated Fair Value	25,505	$ 17,886
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	1,099
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total short-term investments, Estimated Fair Value	$ 1,099