Loans and Leases - Schedule of Changes in Carrying Value of PCI Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Carrying Amount
Balance at beginning of period	$ 3,812,340
Balance at end of period	4,273,415	$ 3,812,340
PCI Loans [Member]
Carrying Amount
Balance at beginning of period	8,892	14,573	$ 43,475
Accretion	602	1,144	2,956
Payments received	(2,827)	(7,138)	(31,215)
Disposal/transfers to OREO	(110)	(977)	(3,772)
Change in expected cash flows, net	0	0	0
Provision for credit losses	651	(664)	(4,415)
Balance at end of period	7,428	8,892	14,573
Accretable Yield
Balance at beginning of period	(5,677)	(5,944)	(11,025)
Accretion	602	1,144	2,956
Payments received	0	0	0
Disposal/transfers to OREO	0	0	0
Change in expected cash flows, net	(410)	(877)	2,125
Provision for credit losses	0	0	0
Balance at end of period	$ (5,485)	$ (5,677)	$ (5,944)