Fair Value (Additional Information) (Details) - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan held for sale, at fair value		$ 8,484,000		$ 8,484,000		$ 15,273,000
Contractual principal balance of loan held for sale		8,291,000		8,291,000		14,983,000
Difference in amount of loan held for sale		193,000		193,000		290,000
Impaired loans, carrying amount	[1]	6,848,000		6,848,000		1,575,000
Valuation allowance for loans losses		1,849,000		1,849,000		355,000
Other real estate, carrying value		0		0		0
Cost of real estate sales		0	$ 75,000	0	$ 75,000	75,000
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		741,710,000		741,710,000		709,786,000
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		6,095,000		6,095,000		7,377,000
Obligations of State and Political Subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total gains/loss included in earnings attributable to other changes in fair value		0	0	34,000	38,000
Obligations of State and Political Subdivisions | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		266,496,000		266,496,000		247,519,000
Total gains/loss included in earnings attributable to other changes in fair value		0	0	34,000	38,000
Obligations of State and Political Subdivisions | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		5,742,000		5,742,000		7,024,000
Equity Securities | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		353,000		353,000		353,000
Total gains/loss included in earnings attributable to other changes in fair value		0	0	0	0
Equity Securities | Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities		353,000		353,000		353,000
Commercial Real Estate Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired loans, carrying amount		6,589,000		6,589,000		663,000
Valuation allowance for loans losses		1,843,000		1,843,000		255,000
Increase (decrease) to provision for loan losses		$ 1,583,000	$ 197,000	$ 1,587,000	$ 222,000	$ 115,000

[1] Unpaid Principal Balance is the remaining contractual principal payments gross of partial charge-offs and discounts.