Loans - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2017 USD ($) Contract	Mar. 31, 2016 USD ($) Contract	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable
Non-covered loans net of unearned premiums, discounts and deferred loan fees	$ 15,700,000		$ 15,300,000
Outstanding balances for PCI loans	1,800,000,000		1,900,000,000
Transfer of loans to loans held for sale	103,884,000	$ 0
Sales of loans	0	0
FDIC loss-share receivable	$ 7,400,000		7,200,000
Number of consecutive months for performing restructured loans to be put on accrual status	6 months
TDRs not reported as non-accrual loans	$ 80,400,000		85,200,000
Non-performing TDRs	13,100,000		10,600,000
Specific reserves for loan losses	2,000,000	1,600,000
Partial loan charge-offs related to loans modified as TDRs	$ 0	$ 209,000
Number of Contracts (in contract) | Contract	4	6
Number of days past due before placed on nonaccrual status	90 days
Recorded Investment	$ 3,128,000	$ 750,000
Other real estate owned	10,700,000		10,200,000
Other real estate owned covered by loss sharing agreements	0		558,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Other real estate owned	2,400,000		1,600,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	5,300,000		7,100,000
Commercial and industrial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Impaired loans	250,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Transfer of loans to loans held for sale	$ 103,900,000
Number of Contracts (in contract) | Contract	1	2
Recorded Investment	$ 321,000	$ 267,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Total PCI Loans including covered loans	$ 47,800,000		$ 70,400,000