Loans and Allowance for Loan Losses - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Commitments to lend additional funds to borrowers whose terms have been modified in a TDR	$ 13,900		$ 15,900
Other real estate owned	16,000		17,000
Residential real estate loans secured by residential real estate properties for which formal foreclosure proceedings were in process	73,000		57,000
Interest Rate Concession
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
TDRs	3,300	$ 465
Modification of Loan Structure
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
TDRs	4,000	$ 84,300
Residential real estate – mortgage
Accounts, Notes, Loans and Financing Receivable Including Other Real Estated Owned [Line Items]
Other real estate owned	$ 11,000		$ 12,000