Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Investments	$ 222,493	$ 100,950
Certificates of deposit
Schedule of Investments [Line Items]
Investments	16,288	11,012
Commercial paper
Schedule of Investments [Line Items]
Investments	15,473	4,997
Corporate debt securities
Schedule of Investments [Line Items]
Investments	185,725	77,441
Securities of government-sponsored entities
Schedule of Investments [Line Items]
Investments	$ 5,007	$ 7,500