Loans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Non-covered loans net of unearned premiums, discounts and deferred loan fees	$ 8,300,000		$ 8,300,000		$ 3,500,000
Outstanding balances for PCI loans	2,100,000,000		2,100,000,000		2,400,000,000
Sales of loans	0	$ 0	0	$ 0
FDIC loss-share receivable	7,600,000		7,600,000		8,300,000
Change in FDIC loss-share receivable	1,000	595,000	$ (559,000)	(3,325,000)
Number of consecutive months for performing restructured loans to be put on accrual status			6 months
TDRs not reported as non-accrual loans	82,100,000		$ 82,100,000		77,600,000
Non-performing TDRs	13,700,000		13,700,000		21,000,000
Specific reserves for loan losses			2,100,000	1,000,000
Partial loan charge-offs related to loans modified as TDRs	0	$ 0	209,000	$ 0
Other real estate owned	12,100,000		12,100,000		19,000,000
Other real estate owned covered by loss sharing agreements	1,200,000		$ 1,200,000		5,000,000
Number Of Days Loans Placed On Non Accrual Status			90 days
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Other real estate owned	6,800,000		$ 6,800,000		7,000,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	9,400,000		9,400,000		12,300,000
Commercial and industrial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Impaired loans	250,000		250,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Total PCI Loans including covered loans	$ 81,100,000		$ 81,100,000		$ 122,300,000