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	Jun. 30, 2016	Dec. 31, 2015
Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 9,291	$ 8,782
Collectively evaluated for impairment	98,797	97,396
Total Loans	108,088	106,178
Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	127,185	132,388
Collectively evaluated for impairment	14,396,594	13,670,248
Total Loans	16,499,180	16,043,107
Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	1,975,401	2,240,471
Commercial and industrial | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,294	3,439
Collectively evaluated for impairment	44,731	45,328
Total Loans	48,025	48,767
Commercial and industrial | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	22,711	25,714
Collectively evaluated for impairment	2,178,127	2,130,835
Total Loans	2,528,749	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	327,911	383,942
Commercial real estate loans | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	4,339	3,671
Collectively evaluated for impairment	47,538	44,335
Total Loans	51,877	48,006
Commercial real estate loans | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	79,353	81,930
Collectively evaluated for impairment	7,375,629	6,595,296
Total Loans	8,787,641	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	1,332,659	1,502,357
Residential mortgage | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,261	1,377
Collectively evaluated for impairment	2,234	3,248
Total Loans	3,495	4,625
Residential mortgage | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	22,654	22,612
Collectively evaluated for impairment	2,834,536	2,889,467
Total Loans	3,055,353	3,130,541
Residential mortgage | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	198,163	218,462
Consumer | Allowance for Loan Losses:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	397	295
Collectively evaluated for impairment	4,294	4,485
Total Loans	4,691	4,780
Consumer | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,467	2,132
Collectively evaluated for impairment	2,008,302	2,054,650
Total Loans	2,127,437	2,192,492
Consumer | Loans acquired with discounts related to credit quality | Loans:
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 116,668	$ 135,710