Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 108,088	$ 102,835	$ 106,178	$ 102,353
Loans charged-off	(5,063)	(2,009)	(9,329)	(11,024)
Charged-off loans recovered	1,723	3,725	5,807	8,840
Net (charge-offs) recoveries	(3,340)	1,716	(3,522)	(2,184)
Provision for loan losses	5,949	0	8,041	4,382
Ending balance	110,697	104,551	110,697	104,551
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	48,025	41,714	48,767	43,676
Loans charged-off	(3,763)	(1,124)	(5,507)	(5,103)
Charged-off loans recovered	902	2,550	2,418	5,587
Net (charge-offs) recoveries	(2,861)	1,426	(3,089)	484
Provision for loan losses	5,588	4,397	5,074	3,377
Ending balance	50,752	47,537	50,752	47,537
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	51,877	44,185	48,006	42,840
Loans charged-off	0	(40)	(519)	(2,780)
Charged-off loans recovered	44	536	1,591	1,686
Net (charge-offs) recoveries	44	496	1,072	(1,094)
Provision for loan losses	539	(2,403)	3,382	532
Ending balance	52,460	42,278	52,460	42,278
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,495	5,055	4,625	5,093
Loans charged-off	(518)	(111)	(750)	(499)
Charged-off loans recovered	495	151	604	395
Net (charge-offs) recoveries	(23)	40	(146)	(104)
Provision for loan losses	(94)	(546)	(1,101)	(440)
Ending balance	3,378	4,549	3,378	4,549
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,691	5,542	4,780	5,179
Loans charged-off	(782)	(734)	(2,553)	(2,642)
Charged-off loans recovered	282	488	1,194	1,172
Net (charge-offs) recoveries	(500)	(246)	(1,359)	(1,470)
Provision for loan losses	(84)	(829)	686	758
Ending balance	4,107	4,467	4,107	4,467
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	6,339	0	5,565
Loans charged-off	0	0	0	0
Charged-off loans recovered	0	0	0	0
Net (charge-offs) recoveries	0	0	0	0
Provision for loan losses		(619)	0	155
Ending balance	$ 0	$ 5,720	$ 0	$ 5,720