Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash accounts, Amount	$ 521,033	$ 427,244
Money market mutual funds, Amount	342,402	356,924
Total	$ 863,435	$ 784,168	$ 760,394	$ 788,064
Cash accounts, % of Total	60.34%	54.48%
Money market mutual funds, % of Total	39.66%	45.52%