Allowance for Credit Losses - Summary of Allocation of Allowance for Loan Losses and Related Loans by Loan Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 9,377	$ 8,782
Collectively evaluated for impairment	96,038	97,396
Total Loans	105,415	106,178
Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	137,579	132,388
Collectively evaluated for impairment	13,882,987	13,670,248
Total Loans	16,135,987	16,043,107
Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	2,115,421	2,240,471
Commercial and industrial | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,578	3,439
Collectively evaluated for impairment	44,839	45,328
Total Loans	48,417	48,767
Commercial and industrial | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	27,596	25,714
Collectively evaluated for impairment	2,149,346	2,130,835
Total Loans	2,537,545	2,540,491
Commercial and industrial | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	360,603	383,942
Commercial real estate loans | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	4,125	3,671
Collectively evaluated for impairment	44,329	44,335
Total Loans	48,454	48,006
Commercial real estate loans | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	85,345	81,930
Collectively evaluated for impairment	6,853,188	6,595,296
Total Loans	8,361,196	8,179,583
Commercial real estate loans | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,422,663	1,502,357
Residential mortgage | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,267	1,377
Collectively evaluated for impairment	2,942	3,248
Total Loans	4,209	4,625
Residential mortgage | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	21,980	22,612
Collectively evaluated for impairment	2,870,663	2,889,467
Total Loans	3,101,814	3,130,541
Residential mortgage | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	209,171	218,462
Consumer | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	407	295
Collectively evaluated for impairment	3,928	4,485
Total Loans	4,335	4,780
Consumer | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,658	2,132
Collectively evaluated for impairment	2,009,790	2,054,650
Total Loans	2,135,432	2,192,492
Consumer | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 122,984	$ 135,710