Loans - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Non-covered loans net of unearned premiums and deferred loan fees	$ 18,700,000		$ 18,700,000		$ 22,200,000
Outstanding balances for PCI loans	4,900,000,000		4,900,000,000		1,500,000,000
Transfer of loans to loans held for sale			263,324,000	$ 225,541,000
Sales of loans	0	$ 0	0	0
Impaired loans	250,000		$ 250,000
Number of consecutive months for performing restructured loans to be put on accrual status			6 months
TDRs not reported as non-accrual loans	83,700,000		$ 83,700,000		117,200,000
Non-performing TDRs	54,100,000		54,100,000		27,000,000
Specific reserves for loan losses			5,300,000	5,300,000
Partial loan charge-offs related to loans modified as TDRs	$ 0	0	$ 0	0
Days past due to place on payment default	90 days		90 days
Recorded Investment	$ 3,212,000	$ 5,358,000	$ 3,212,000	6,322,000
Other real estate owned	11,800,000		11,800,000		9,800,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Other real estate owned	8,100,000		8,100,000		7,300,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	1,800,000		1,800,000		3,800,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Transfer of loans to loans held for sale			263,300,000	225,500,000
Recorded Investment			0	$ 153,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Total PCI Loans including covered loans	$ 31,100,000		$ 31,100,000		$ 38,700,000