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	Sep. 30, 2016	Dec. 31, 2015
Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 8,999	$ 8,782
Collectively evaluated for impairment	101,698	97,396
Total Loans	110,697	106,178
Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	116,448	132,388
Collectively evaluated for impairment	14,660,572	13,670,248
Total Loans	16,634,135	16,043,107
Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,857,115	2,240,471
Commercial and industrial | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,506	3,439
Collectively evaluated for impairment	47,246	45,328
Total Loans	50,752	48,767
Commercial and industrial | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	27,128	25,714
Collectively evaluated for impairment	2,239,292	2,130,835
Total Loans	2,558,968	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	292,548	383,942
Commercial real estate loans | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	4,575	3,671
Collectively evaluated for impairment	47,885	44,335
Total Loans	52,460	48,006
Commercial real estate loans | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	69,089	81,930
Collectively evaluated for impairment	7,780,548	6,595,296
Total Loans	9,116,423	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	1,266,786	1,502,357
Residential mortgage | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	708	1,377
Collectively evaluated for impairment	2,670	3,248
Total Loans	3,378	4,625
Residential mortgage | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	18,508	22,612
Collectively evaluated for impairment	2,618,803	2,889,467
Total Loans	2,826,130	3,130,541
Residential mortgage | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	188,819	218,462
Consumer | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	210	295
Collectively evaluated for impairment	3,897	4,485
Total Loans	4,107	4,780
Consumer | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,723	2,132
Collectively evaluated for impairment	2,021,929	2,054,650
Total Loans	2,132,614	2,192,492
Consumer | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 108,962	$ 135,710