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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 171,185	$ 71,422	$ 184,618	$ 76,518
Interest income	(14,060)	(5,772)	(28,122)	(10,978)
Reclassifications from nonaccretable balance, net	4,898	11,974	5,527	12,084
Balance at end of period	162,023	77,624	162,023	77,624
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	269,017	357,895	296,434	397,379
Interest income	(32,898)	(40,024)	(70,760)	(81,301)
Reclassifications from nonaccretable balance, net	2,933	26,840	8,597	27,023
Other	6,143	278	10,924	1,888
Balance at end of period	$ 245,195	$ 344,989	$ 245,195	$ 344,989