Loans and Leases and the Allowance for Credit Losses - Summary of Changes in Accretable Yield for Acquired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 162,023	$ 77,624	$ 184,618	$ 76,518
Interest income	(12,784)	(5,865)	(40,906)	(16,843)
Reclassifications from nonaccretable balance	2,256	47	7,783	12,131
Balance at end of period	151,495	71,806	151,495	71,806
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	245,195	344,989	296,434	397,379
Interest income	(26,540)	(37,396)	(97,300)	(118,697)
Reclassifications from nonaccretable balance	12,050	769	20,647	27,792
Other	(818)	4,697	10,106	6,585
Balance at end of period	$ 229,887	$ 313,059	$ 229,887	$ 313,059