Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 105,415	$ 102,631	$ 106,178	$ 102,353
Loans charged-off	(1,755)	(7,349)	(4,266)	(9,015)
Charged-off loans recovered	3,065	3,171	4,084	5,115
Net (charge-offs) recoveries	1,310	(4,178)	(182)	(3,900)
Provision for loan losses	1,363	4,382	2,092	4,382
Ending balance	108,088	102,835	108,088	102,835
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	48,417	44,893	48,767	43,676
Loans charged-off	(493)	(3,226)	(1,744)	(3,979)
Charged-off loans recovered	990	1,986	1,516	3,037
Net (charge-offs) recoveries	497	(1,240)	(228)	(942)
Provision for loan losses	(889)	(1,939)	(514)	(1,020)
Ending balance	48,025	41,714	48,025	41,714
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	48,454	41,656	48,006	42,840
Loans charged-off	(414)	(2,590)	(519)	(2,740)
Charged-off loans recovered	1,458	690	1,547	1,150
Net (charge-offs) recoveries	1,044	(1,900)	1,028	(1,590)
Provision for loan losses	2,379	4,429	2,843	2,935
Ending balance	51,877	44,185	51,877	44,185
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,209	4,092	4,625	5,093
Loans charged-off	(151)	(339)	(232)	(388)
Charged-off loans recovered	94	130	109	244
Net (charge-offs) recoveries	(57)	(209)	(123)	(144)
Provision for loan losses	(657)	1,172	(1,007)	106
Ending balance	3,495	5,055	3,495	5,055
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,335	4,972	4,780	5,179
Loans charged-off	(697)	(1,194)	(1,771)	(1,908)
Charged-off loans recovered	523	365	912	684
Net (charge-offs) recoveries	(174)	(829)	(859)	(1,224)
Provision for loan losses	530	1,399	770	1,587
Ending balance	4,691	5,542	4,691	5,542
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	7,018	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	0	(679)	0	774
Ending balance	$ 0	$ 6,339	$ 0	$ 6,339