Loans - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Number Of Days Loans Placed On Non Accrual Status	90 days
Non-covered loans net of unearned premiums, discounts and deferred loan fees	$ 5,600,000		$ 3,500,000
Loans	16,135,987,000		16,043,107,000
Sales of loans	0	$ 0
FDIC loss-share receivable	7,300,000		8,300,000
Change in FDIC loss-share receivable	$ (560,000)	(3,920,000)
Combined loan-to-value ratio home equity loan	75.00%
TDRs not reported as non-accrual loans	$ 80,500,000		77,600,000
Non-performing TDRs	19,400,000		21,000,000
Specific reserves for loan losses	1,600,000	759,000
Partial loan charge-offs related to loans modified as TDRs	209,000	$ 0
Repossessed Assets	14,700,000		19,000,000
Repossessed assets covered by loss sharing agreements	2,400,000		5,000,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Repossessed Assets	7,200,000		7,000,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	13,300,000		12,300,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Unsecured loans	402,700,000		386,600,000
Commercial and industrial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Impaired loans	250,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	2,300,000,000		2,400,000,000
Consumer loans
Accounts, Notes, Loans and Financing Receivable
Unsecured loans	20,400,000		18,800,000
Credit card loans
Accounts, Notes, Loans and Financing Receivable
Unsecured loans	$ 6,600,000		$ 7,100,000