Loans (Textual) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Segment tenant loan employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of portfolio segment | Segment	2
Number of classes of loans | loan	6
Minimum number of tenants leased to for non-owner occupied real estate | tenant	1
Loans held-for-sale, at fair value	$ 52,133	$ 81,830
Loans held-for-sale, recorded investment sold	806,800	707,800	$ 222,600
Minimum value of loan requires regional loan committee approval	3,000
Maximum value of loan requires regional loan committee approval	$ 7,000
Minimum due period of loans consider in a nonperforming status	90 days
Nonaccrual TDRs reported in nonaccrual loans	$ 29,100	30,500
Interest income recognized on nonaccrual loans while in accruing status	1,300	400	900
Interest lost on nonaccrual loans	3,100	2,900	3,200
Interest income recognized on TDRs	2,600	3,900	$ 3,900
Real estate properties for which formal foreclosure proceedings are in process	4,200
Residential mortgage loans in process of foreclosure		7,300
Impaired loans	77,888	93,066
Commitments to lend additional funds to borrowers whose terms have been modified in TDRs	2,000
Management
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans to directors, executive officers and affiliates	3,800	23,900
Loans to directors, executive officers and affiliates, current year additions	44,100	33,800
Loans to directors, executive officers and affiliates, current year reductions	64,200	31,600
Fixed-Rate Real Estate Residential Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held-for-sale, at fair value		81,800
Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	48,782	62,535
Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	58,842	70,785
Commercial Loan Portfolio | Performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	$ 34,484	$ 45,388
Land Development Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum period for payment of loan	12 months
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for loan secured under real estate residential security	15 years
Loan-to-value ratio at the time of origination	80.00%
Residential mortgage | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lower limit of number of family residential properties | tenant	1
Residential mortgage | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Upper limit of number of family residential properties | tenant	4
Commercial | Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum value of loan requires group loan authority approval	$ 3,000
Number of bank executives and senior officers with credit decision limits similar to group loan authorities | employee	6
Maximum value of loan requires executive and senior officer approval	$ 8,000
Minimum value of loan requires group loan authority approval	$ 5,000
Commercial Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum due period of loans consider in a nonperforming status	90 days
Consumer Loan Portfolio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Original contractual terms	90 days
Minimum due period of loans consider in a nonperforming status	90 days