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, 2017	Mar. 31, 2016
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 154,233	$ 184,618
Interest income	(10,925)	(14,062)
Reclassifications from nonaccretable balance	146	629
Balance at end of period	143,454	171,185
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	201,153	296,434
Interest income	(25,518)	(37,862)
Reclassifications from nonaccretable balance	3,183	5,664
Other	2,492	4,781
Balance at end of period	$ 181,310	$ 269,017