Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	[1]	Dec. 31, 2013	[1],[2]
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 1,454,538	$ 1,694,329
Securities purchased under agreements to resell	214,484	95,611
Other short-term investment securities	5,123	6,122
Total cash and cash equivalents	$ 1,674,145	$ 1,796,062	$ 1,872,537		$ 1,538,779

[1] Cash flows for the nine months ended September 30, 2015 were revised to reflect the adoption of ASU 2015-02 as of January 1, 2015 and cash flows for the nine months ended September 30, 2014 were revised to reflect the retrospective application of our adoption of ASU 2014-01.

[2] 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.