Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013	[1]
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 2,281,816	$ 1,694,329
Securities purchased under agreements to resell	338,612	95,611
Other short-term investment securities	5,122	6,122
Total cash and cash equivalents	$ 2,625,550	$ 1,796,062	$ 2,649,831	$ 1,538,779

[1] Cash and cash equivalents at December 31, 2014 included $15.0 million recognized in assets held-for-sale in conjunction with the SVBIF Sale Transaction. On April 13, 2015 we received net proceeds of $39.3 million consisting of the sales price of $48.6 million less $9.3 million of cash and cash equivalents held by SVBIF that were sold.