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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Purchased Impaired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	$ 143,454	$ 171,185	$ 154,233	$ 184,618
Interest income	(10,806)	(14,060)	(21,731)	(28,122)
Reclassifications from nonaccretable balance	884	4,898	1,030	5,527
Balance at end of period	133,532	162,023	133,532	162,023
Other Acquired [Member]
Summary of changes in Accretable Yield for acquired loans
Balance at beginning of period	181,310	269,017	201,153	296,434
Interest income	(20,923)	(32,898)	(46,441)	(70,760)
Reclassifications from nonaccretable balance	1,852	2,933	5,035	8,597
Other	860	6,143	3,352	10,924
Balance at end of period	$ 163,099	$ 245,195	$ 163,099	$ 245,195