Investments - Summary of Short-Term Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Maturity weighted average period, in years (less than)	2 years
Amortized cost	$ 98,184	$ 122,580
Unrealized Gains	22	3
Unrealized Losses	(103)	(167)
Estimated fair value	$ 98,103	$ 122,416
Corporate debt securities
Investment [Line Items]
Maturity (or less) (in years)	2 years	2 years
Amortized cost	$ 81,054	$ 105,085
Unrealized Gains	16	2
Unrealized Losses	(103)	(167)
Estimated fair value	$ 80,967	$ 104,920
Certificates of deposit
Investment [Line Items]
Maturity (or less) (in years)	2 years	2 years
Amortized cost	$ 13,640	$ 14,600
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated fair value	$ 13,640	$ 14,600
Commercial paper
Investment [Line Items]
Maturity (or less) (in years)	1 year	1 year
Amortized cost	$ 3,490	$ 2,895
Unrealized Gains	6	1
Unrealized Losses	0	0
Estimated fair value	$ 3,496	$ 2,896