Cash, Cash Equivalents, and Short-Term Investments - Summary of Cost and Estimated Fair Value of Short-Term Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Short Term Investments [Abstract]
Amortized Cost of short-term investments, Due in 2016	$ 53,086
Amortized Cost of short-term investments, Due in 2017	43,767
Short-term investments, Amortized Cost	96,853	$ 41,674
Estimated fair value of short-term investments, Due in 2016	53,003
Estimated fair value of short-term investments, Due in 2017	43,552
Short-term investments, Estimated Fair Value	$ 96,555	$ 41,624