Federal Funds Purchased and Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Federal Funds Purchased	$ 30,000	$ 80,000	$ 0
Securities Sold under Agreements to Repurchase	32,169	59,624	58,215
Available-for-sale Securities Pledged as Collateral	144,300	182,700
Federal Funds Lines of Credit, Amount of Available Unused Funds	435,000	485,000
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Short-term Debt, Maximum Month-end Outstanding Amount	100,000	180,000	102,000
Short-term Debt, Average Outstanding Amount	$ 22,742	$ 29,542	$ 10,008
Short-term Debt, Weighted Average Interest Rate, at Point in Time	1.50%	0.75%	0.00%
Debt Instrument, Interest Rate During Period	1.19%	0.54%	0.31%
Securities Sold under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Short-term Debt, Maximum Month-end Outstanding Amount	$ 67,249	$ 77,466	$ 75,313
Short-term Debt, Average Outstanding Amount	$ 58,872	$ 66,282	$ 64,320
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.09%	0.05%	0.05%
Debt Instrument, Interest Rate During Period	0.09%	0.05%	0.05%