Securities Sold Under Agreements to Repurchase and Federal Funds Purchased (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retail Repurchase Agreements
Repurchase Agreement Counterparty [Line Items]
Total outstanding at December 31	$ 75,200,000
Wholesale Repurchase Agreements
Repurchase Agreement Counterparty [Line Items]
Total outstanding at December 31	0
Securities Sold Under Agreements to Repurchase
Repurchase Agreement Counterparty [Line Items]
Total outstanding at December 31	75,177,000	$ 69,062,000	$ 136,513,000
Maximum month-end balance	80,326,000	125,063,000	146,397,000
Average balance during the year	$ 64,888,000	$ 99,622,000	$ 137,917,000
Weighted average rate at December 31	0.23%	0.88%	1.90%
Average interest rate paid during the year	0.36%	2.24%	1.96%
Federal Funds Purchased
Repurchase Agreement Counterparty [Line Items]
Average balance during the year	$ 0	$ 0	$ 0
Average interest rate paid during the year	0.00%	0.00%	0.00%