Rollforward of Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 80,398	$ 77,479	$ 81,143	$ 76,140
Charge-offs	(4,252)	(5,602)	(13,287)	(8,750)
Recoveries	1,520	844	4,810	2,331
Provision	7,000	5,000	12,000	8,000
Ending balance	84,666	77,721	84,666	77,721
Ending balance: individually evaluated for impairment	4,740	1,561	4,740	1,561	$ 5,864
Ending balance: collectively evaluated for impairment	79,926	76,160	79,926	76,160
Total Loans	10,083,266	8,916,128	10,083,266	8,916,128	9,430,761
Ending balance: individually evaluated for impairment	67,186	43,171	67,186	43,171
Ending balance: collectively evaluated for impairment	10,013,858	8,865,265	10,013,858	8,865,265
Ending balance: PCI Loans	2,222	7,692	2,222	7,692
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	61,308	55,659	63,847	55,349
Charge-offs	(800)	(3,088)	(5,875)	(3,500)
Recoveries	859	89	3,348	899
Provision	3,194	6,718	3,241	6,630
Ending balance	64,561	59,378	64,561	59,378
Ending balance: individually evaluated for impairment	4,714	1,266	4,714	1,266
Ending balance: collectively evaluated for impairment	59,847	58,112	59,847	58,112
Total Loans	4,914,162	4,579,611	4,914,162	4,579,611
Ending balance: individually evaluated for impairment	58,270	32,818	58,270	32,818
Ending balance: collectively evaluated for impairment	4,855,892	4,544,303	4,855,892	4,544,303
Ending balance: PCI Loans		2,490		2,490
Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,909	11,912	8,220	10,725
Charge-offs	(1,351)	(68)	(2,796)	(100)
Recoveries	187	77	331	92
Provision	1,938	(3,029)	4,928	(1,825)
Ending balance	10,683	8,892	10,683	8,892
Ending balance: individually evaluated for impairment	26	295	26	295
Ending balance: collectively evaluated for impairment	10,657	8,597	10,657	8,597
Total Loans	4,737,311	3,915,506	4,737,311	3,915,506
Ending balance: individually evaluated for impairment	6,338	9,113	6,338	9,113
Ending balance: collectively evaluated for impairment	4,729,981	3,903,880	4,729,981	3,903,880
Ending balance: PCI Loans	992	2,513	992	2,513
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,060	9,780	8,949	9,921
Charge-offs	(2,101)	(2,446)	(4,616)	(5,150)
Recoveries	474	678	1,131	1,340
Provision	1,886	1,276	3,855	3,177
Ending balance	9,319	9,288	9,319	9,288
Ending balance: collectively evaluated for impairment	9,319	9,288	9,319	9,288
Total Loans	395,216	380,938	395,216	380,938
Ending balance: individually evaluated for impairment	2,578	1,240	2,578	1,240
Ending balance: collectively evaluated for impairment	391,408	377,009	391,408	377,009
Ending balance: PCI Loans	1,230	2,689	1,230	2,689
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	121	128	127	145
Provision	(18)	35	(24)	18
Ending balance	103	163	103	163
Ending balance: collectively evaluated for impairment	103	163	103	163
Total Loans	36,577	40,073	36,577	40,073	$ 41,857
Ending balance: collectively evaluated for impairment	$ 36,577	$ 40,073	$ 36,577	$ 40,073