Allowance for Credit Losses - Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 115,443	$ 105,415	$ 114,419	$ 106,178
Loans charged-off	(4,289)	(1,755)	(7,668)	(4,266)
Charged-off loans recovered	1,582	3,065	3,583	4,084
Net (charge-offs) recoveries	(2,707)	1,310	(4,085)	(182)
Provision for loan losses	3,710	1,363	6,112	2,092
Ending balance	116,446	108,088	116,446	108,088
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	51,288	48,417	50,820	48,767
Loans charged-off	(2,910)	(493)	(4,624)	(1,744)
Charged-off loans recovered	312	990	1,160	1,516
Net (charge-offs) recoveries	(2,598)	497	(3,464)	(228)
Provision for loan losses	2,927	(889)	4,261	(514)
Ending balance	51,617	48,025	51,617	48,025
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	56,302	48,454	55,851	48,006
Loans charged-off	(139)	(414)	(553)	(519)
Charged-off loans recovered	640	1,458	782	1,547
Net (charge-offs) recoveries	501	1,044	229	1,028
Provision for loan losses	(1,348)	2,379	(625)	2,843
Ending balance	55,455	51,877	55,455	51,877
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	3,592	4,209	3,702	4,625
Loans charged-off	(229)	(151)	(359)	(232)
Charged-off loans recovered	235	94	683	109
Net (charge-offs) recoveries	6	(57)	324	(123)
Provision for loan losses	588	(657)	160	(1,007)
Ending balance	4,186	3,495	4,186	3,495
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,261	4,335	4,046	4,780
Loans charged-off	(1,011)	(697)	(2,132)	(1,771)
Charged-off loans recovered	395	523	958	912
Net (charge-offs) recoveries	(616)	(174)	(1,174)	(859)
Provision for loan losses	1,543	530	2,316	770
Ending balance	$ 5,188	$ 4,691	$ 5,188	$ 4,691