Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Investments	$ 387,484	$ 200,287
Certificates of deposit
Schedule of Investments [Line Items]
Investments	10,078	17,438
Commercial paper
Schedule of Investments [Line Items]
Investments	23,955	7,498
Corporate debt securities
Schedule of Investments [Line Items]
Investments	323,219	174,323
Securities of government sponsored entities
Schedule of Investments [Line Items]
Investments	$ 30,232	$ 1,028