Acquisitions and FDIC Indemnification Asset (Details Textual) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Gain on Sale of certain assets and liabilities of Insurance Brokerage Operation	$ 0	$ 0
Assets	2,956,653,000		$ 3,000,668,000
Goodwill	34,355,000		34,355,000
Loans and Leases Receivable, Net of Loans with Deteriorated Credit Quality, Covered	4,000,000		4,300,000
First National Bank Of Danville [Member]
Business Acquisition [Line Items]
Reimbursements from the FDIC	19,400,000
Business Aquisition, Loss Sharing Agreement Losses On Assets Threshold	$ 29,000,000
Business Acquisition Loss Sharing Agreement Losses In Excess Of Threshold To Be Reimbursed Percentage	95.00%
Business Acquisition, Loss Sharing Agreement Losses Up To Threshold To Be Reimbursed Percentage	80.00%
Forrest Sherer Insurance [Domain]
Business Acquisition [Line Items]
Assets			13,000,000	$ 15,800,000
Insurance Services Revenue			7,600,000	8,300,000
Operating Income (Loss)			$ 168,000	$ 554,000