Allowance for Credit Losses - Allocation of Allowance for Loan Losses and Related Loans by Segment (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 10,348	$ 10,531
Collectively evaluated for impairment	106,098	103,888
Total Loans	116,446	114,419
Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	145,993	114,819
Collectively evaluated for impairment	16,023,298	15,349,782
Total Loans	17,710,760	17,236,103
Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,541,469	1,771,502
Commercial and industrial | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	6,746	5,864
Collectively evaluated for impairment	44,871	44,956
Total Loans	51,617	50,820
Commercial and industrial | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	60,237	30,640
Collectively evaluated for impairment	2,357,687	2,326,378
Total Loans	2,631,312	2,638,195
Commercial and industrial | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	213,388	281,177
Commercial Real Estate | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,969	3,872
Collectively evaluated for impairment	52,486	51,979
Total Loans	55,455	55,851
Commercial Real Estate | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	66,016	62,289
Collectively evaluated for impairment	8,960,415	8,276,305
Total Loans	10,111,587	9,544,613
Commercial Real Estate | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,085,156	1,206,019
Residential mortgage | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	582	725
Collectively evaluated for impairment	3,604	2,977
Total Loans	4,186	3,702
Residential mortgage | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	16,189	18,356
Collectively evaluated for impairment	2,553,311	2,665,839
Total Loans	2,724,777	2,867,918
Residential mortgage | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	155,277	183,723
Consumer | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	51	70
Collectively evaluated for impairment	5,137	3,976
Total Loans	5,188	4,046
Consumer | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,551	3,534
Collectively evaluated for impairment	2,151,885	2,081,260
Total Loans	2,243,084	2,185,377
Consumer | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 87,648	$ 100,583