Fair Value of Financial Instruments - Financial Instruments Measured at Fair Value on Recurring Basis by Level within Fair Value Hierarchy (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financial Assets
Marketable securities available-for-sale	$ 51,009	$ 164,619
Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	18,903	9,708
Marketable securities available-for-sale	51,009	164,619
Financial Assets Total	69,912	174,327
Financial Liabilities
Derivative Liability	82	83
Level 1 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	3	1,880
Marketable securities available-for-sale	3,722	4,897
Financial Assets Total	3,725	6,777
Financial Liabilities
Derivative Liability	0	0
Level 2 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	18,900	7,828
Marketable securities available-for-sale	47,287	159,722
Financial Assets Total	66,187	167,550
Financial Liabilities
Derivative Liability	0	0
Level 3 | Fair Value, Measurements, Recurring
Financial Assets
Cash equivalents	0	0
Marketable securities available-for-sale	0	0
Financial Assets Total	0	0
Financial Liabilities
Derivative Liability	$ 82	$ 83