Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Investments	$ 165,650	$ 100,950
Certificates of deposit
Schedule of Investments [Line Items]
Investments	11,217	11,012
Commercial paper
Schedule of Investments [Line Items]
Investments	19,964	4,997
Corporate debt securities
Schedule of Investments [Line Items]
Investments	121,940	77,441
Securities of government-sponsored entities
Schedule of Investments [Line Items]
Investments	$ 12,529	$ 7,500