Marketable Securities Marketable Securities Classified as Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 82,574	$ 112,458
Gross Unrealized Gain	119	131
Gross Unrealized Loss	(45)	(45)
Fair Value	82,648	112,544
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,328	45,414
Gross Unrealized Gain	47	75
Gross Unrealized Loss	(6)	(7)
Fair Value	34,369	45,482
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,761	21,222
Gross Unrealized Gain	15	12
Gross Unrealized Loss	(2)	(8)
Fair Value	17,774	21,226
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,528	15,110
Gross Unrealized Gain	40	33
Gross Unrealized Loss	(27)	(26)
Fair Value	13,541	15,117
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,545	12,255
Gross Unrealized Gain	14	9
Gross Unrealized Loss	(9)	0
Fair Value	8,550	12,264
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,596	13,890
Gross Unrealized Gain	1	2
Gross Unrealized Loss	0	0
Fair Value	4,597	13,892
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,816	3,817
Gross Unrealized Gain	2	0
Gross Unrealized Loss	(1)	(4)
Fair Value	3,817	3,813
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		750
Gross Unrealized Gain		0
Gross Unrealized Loss		0
Fair Value		$ 750