Summary of Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 33,457	$ 36,834
Gross Unrealized (Loss) Gain	(31)	7
Fair Value	33,426	36,841
Money market funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,912	8,650
Gross Unrealized (Loss) Gain	0	0
Fair Value	3,912	8,650
United States government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,427	5,019
Gross Unrealized (Loss) Gain	(1)	(1)
Fair Value	3,426	5,018
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,118	23,165
Gross Unrealized (Loss) Gain	(30)	8
Fair Value	$ 26,088	$ 23,173