Acquisitions - Narrative (Details) - USD ($)				12 Months Ended
	Oct. 01, 2016	Jun. 01, 2016	Feb. 29, 2016	Dec. 31, 2016	Dec. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Preliminary goodwill resulting from acquisition				$ 10,989,000			$ 6,198,000
Acquisition related expenses				933,000
HCB and Subsidiary
Business Acquisition [Line Items]
Percentage of ownership acquired	100.00%
Price paid in acquisition (in USD per share)			$ 38.00
Consideration paid in acquisition			$ 21,800,000
Value of assets acquired						$ 123,000,000
Value of liabilities acquired						$ 107,000,000
Preliminary goodwill resulting from acquisition	$ 4,790,000
HCB and Subsidiary | Core Deposits
Business Acquisition [Line Items]
Weighted average life of intangibles acquired	16 years
FCB
Business Acquisition [Line Items]
Price paid in acquisition (in USD per share)		$ 22.50
Value of assets acquired					$ 405,000,000
Acquisition related expenses				400,000
Value of consideration (in shares)		1.2433
Percent of cash to be received in business combination		35.00%
Percent of stock to be received in business combination		65.00%
Defined benefit plan termination expense				5,460,000
Highland County Bankshares, Inc [Member]
Business Acquisition [Line Items]
Value of assets acquired	$ 122,840,000
Value of liabilities acquired	$ 107,239,000
Acquisition related expenses				$ 405,000