Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash and due from banks	$ 3,658,927	$ 2,476,588
Securities purchased under agreements to resell	192,421	64,028
Other short-term investment securities	2,896	5,134
Total cash and cash equivalents	$ 3,854,244	$ 2,545,750	$ 1,854,457	$ 1,503,257