Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	$ 106,178	$ 102,353
Loans charged-off	(10,969)	(14,972)
Charged-off loans recovered	7,337	10,951
Net charge-offs	(3,632)	(4,021)
Provision for loan losses	11,873	7,846
Ending balance	114,419	106,178
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	48,767	43,676
Loans charged-off	(5,990)	(7,928)
Charged-off loans recovered	2,852	7,233
Net charge-offs	(3,138)	(695)
Provision for loan losses	5,191	5,786
Ending balance	50,820	48,767
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	48,006	42,840
Loans charged-off	(650)	(2,790)
Charged-off loans recovered	2,057	1,759
Net charge-offs	1,407	(1,031)
Provision for loan losses	6,438	6,197
Ending balance	55,851	48,006
Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,625	5,093
Loans charged-off	(866)	(813)
Charged-off loans recovered	774	421
Net charge-offs	(92)	(392)
Provision for loan losses	(831)	(76)
Ending balance	3,702	4,625
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	4,780	5,179
Loans charged-off	(3,463)	(3,441)
Charged-off loans recovered	1,654	1,538
Net charge-offs	(1,809)	(1,903)
Provision for loan losses	1,075	1,504
Ending balance	4,046	4,780
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning balance	0	5,565
Loans charged-off	0	0
Charged-off loans recovered	0	0
Net charge-offs	0	0
Provision for loan losses		(5,565)
Ending balance	$ 0	$ 0