Loans - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) Contract	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable
Non-covered loans net of unearned premiums, discounts and deferred loan fees	$ 10,500,000		$ 10,500,000		$ 3,500,000
Outstanding balances for PCI loans	2,000,000,000		2,000,000,000		2,400,000,000
Transfer of loans to loans held for sale			174,501,000	$ 0
Sales of loans	0	$ 0	0	0
FDIC loss-share receivable	7,700,000		7,700,000		8,300,000
Change in FDIC loss-share receivable	(313,000)	(55,000)	$ (872,000)	(3,380,000)
Number of consecutive months for performing restructured loans to be put on accrual status			6 months
TDRs not reported as non-accrual loans	81,100,000		$ 81,100,000		77,600,000
Non-performing TDRs	13,000,000		13,000,000		21,000,000
Specific reserves for loan losses			2,400,000	602,000
Partial loan charge-offs related to loans modified as TDRs	0	0	$ 209,000	0
Number of days past due before placed on nonaccrual status			90 days
Other real estate owned	11,300,000		$ 11,300,000		19,000,000
Other real estate owned covered by loss sharing agreements	1,000,000		1,000,000		5,000,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Other real estate owned	7,400,000		7,400,000		7,000,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	7,700,000		7,700,000		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	76,000,000		76,000,000		$ 122,300,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Transfer of loans to loans held for sale	$ 174,500,000
Number of Contracts (in contract) | Contract	4
Recorded Investment	$ 1,100,000	$ 0	$ 1,100,000	$ 0