Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Cash accounts, Amount	$ 503,107	$ 427,244
Money market mutual funds, Amount	334,809	356,924
Total	$ 837,916	$ 784,168	$ 776,239	$ 788,064
Cash accounts, % of Total	60.04%	54.48%
Money market mutual funds, % of Total	39.96%	45.52%