Marketable Securities, Available for Sale - Summary of Available-for-Sale Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 17,035	$ 37,647
Unrealized Gain	4	1
Unrealized Loss	3	9
Market Value	17,036	37,639
U.S. treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,008	10,135
Unrealized Gain	4	1
Unrealized Loss
Market Value	4,012	10,136
Government-sponsored enterprise securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,000	15,507
Unrealized Gain
Unrealized Loss		1
Market Value	7,000	15,506
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,856	11,509
Unrealized Gain
Unrealized Loss	3	8
Market Value	4,853	11,501
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,171	496
Unrealized Gain
Unrealized Loss
Market Value	$ 1,171	$ 496