Marketable Securities Marketable Securities Classified as Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 204,768	$ 112,458
Gross Unrealized Gain	158	131
Gross Unrealized Loss	(124)	(45)
Fair Value	204,802	112,544
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	75,986	45,414
Gross Unrealized Gain	59	75
Gross Unrealized Loss	(49)	(7)
Fair Value	75,996	45,482
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	60,026	21,222
Gross Unrealized Gain	39	12
Gross Unrealized Loss	(12)	(8)
Fair Value	60,053	21,226
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,115	15,110
Gross Unrealized Gain	43	33
Gross Unrealized Loss	(38)	(26)
Fair Value	22,120	15,117
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,533	13,890
Gross Unrealized Gain	6	2
Gross Unrealized Loss	0	0
Fair Value	32,539	13,892
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,397	12,255
Gross Unrealized Gain	10	9
Gross Unrealized Loss	(22)	0
Fair Value	11,385	12,264
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,711	3,817
Gross Unrealized Gain	1	0
Gross Unrealized Loss	(3)	(4)
Fair Value	2,709	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