Allowance for Credit Losses - Allocation of Allowance for Loan Losses and Related Loans by Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 9,843	$ 10,531
Collectively evaluated for impairment	105,600	103,888
Total Loans	115,443	114,419
Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	112,485	114,819
Collectively evaluated for impairment	15,682,312	15,349,782
Total Loans	17,449,498	17,236,103
Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,654,701	1,771,502
Commercial and industrial | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	5,688	5,864
Collectively evaluated for impairment	45,600	44,956
Total Loans	51,288	50,820
Commercial and industrial | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	30,061	30,640
Collectively evaluated for impairment	2,368,094	2,326,378
Total Loans	2,642,320	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	244,165	281,177
Commercial real estate loans | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,376	3,872
Collectively evaluated for impairment	52,926	51,979
Total Loans	56,302	55,851
Commercial real estate loans | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	60,083	62,289
Collectively evaluated for impairment	8,649,408	8,276,305
Total Loans	9,852,271	9,544,613
Commercial real estate loans | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,142,780	1,206,019
Residential mortgage | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	686	725
Collectively evaluated for impairment	2,906	2,977
Total Loans	3,592	3,702
Residential mortgage | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	18,557	18,356
Collectively evaluated for impairment	2,555,789	2,665,839
Total Loans	2,745,447	2,867,918
Residential mortgage | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	171,101	183,723
Consumer | Allowance for loan losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	93	70
Collectively evaluated for impairment	4,168	3,976
Total Loans	4,261	4,046
Consumer | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,784	3,534
Collectively evaluated for impairment	2,109,021	2,081,260
Total Loans	2,209,460	2,185,377
Consumer | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 96,655	$ 100,583