Loans - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Non-covered loans net of unearned premiums and deferred loan fees	$ 16,700,000		$ 16,700,000		$ 22,200,000
Outstanding balances for PCI loans	4,600,000,000		4,600,000,000		1,500,000,000
Transfer of loans to loans held for sale			289,633,000	$ 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	81,100,000		$ 81,100,000		117,200,000
Non-performing TDRs	54,800,000		54,800,000		27,000,000
Specific reserves for loan losses			6,300,000	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
Other real estate owned	$ 9,900,000		$ 9,900,000		9,800,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable
Other real estate owned	1,600,000		1,600,000		7,300,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable
Residential mortgage and consumer loans secured by residential real estate properties	$ 2,200,000		2,200,000		$ 3,800,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Transfer of loans to loans held for sale			$ 289,600,000	$ 225,500,000