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
	Mar. 31, 2016	Mar. 31, 2015
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 481,052	$ 473,897
Interest income	(51,924)	(46,483)
Reclassifications from nonaccretable balance, net	6,293	293
Other	4,781	1,610
Balance at end of period	440,202	429,317
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	184,618	76,518
Interest income	(14,062)	(5,206)
Reclassifications from nonaccretable balance, net	629	110
Balance at end of period	171,185	71,422
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	296,434	397,379
Interest income	(37,862)	(41,277)
Reclassifications from nonaccretable balance, net	5,664	183
Other	4,781	1,610
Balance at end of period	$ 269,017	$ 357,895