Condensed Financial Information (Parent Company Only) Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 2,345	$ 2,268	$ 2,139	$ 1,759	$ 1,927	$ 2,050	$ 2,017	$ 1,884	$ 1,885	$ 2,126	$ 1,919	$ 1,764	$ 8,511	$ 7,878	$ 7,694
Adjustments to reconcile net income to net cash provided by operating activities
Stock based compensation expense													66	35	20
Net gains on sale of investment securities available-for-sale													(71)	(53)	(315)
Decrease (increase) in other assets													(1,202)	(1,387)	1,849
Net cash provided by operating activities													7,644	13,130	2,204
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of investment securities available-for-sale													6,620	11,540	7,420
Purchases of investment securities available-for-sale													(29,098)	(27,416)	(21,921)
Proceeds of Company-owned life insurance death benefit													527	0	0
Net cash provided by investing activities													(40,724)	(34,846)	(22,148)
CASH FLOWS FROM FINANCING ACTIVITIES
Dividends paid													(4,939)	(4,816)	(4,637)
Issuance of common stock													56	53	39
Purchase of treasury stock													(6)	(94)	(45)
Net cash used in financing activities													54,394	(2,067)	30,969
Net (decrease) increase in cash													21,314	(23,783)	11,025
Supplemental Disclosures of Cash Flow Information
Interest paid													2,239	2,060	2,146
Dividends paid on Common Stock [Abstract]
Dividends declared													4,949	4,816	4,637
Dividends reinvested													(10)	0	0
Dividends paid on Common Stock													4,939	4,816	4,637
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net income													8,511	7,878	7,694
Adjustments to reconcile net income to net cash provided by operating activities
Equity in undistributed net income - Union													(3,734)	(3,038)	(3,011)
Stock based compensation expense													0	35	20
Net gains on sale of investment securities available-for-sale													0	0	(20)
Decrease (increase) in other assets													38	50	(71)
(Decrease) increase in other liabilities													(45)	(67)	30
Net cash provided by operating activities													4,770	4,858	4,642
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sale of investment securities available-for-sale													16	16	56
Purchases of investment securities available-for-sale													(4)	(1)	(17)
Proceeds of Company-owned life insurance death benefit													99	0	0
Net cash provided by investing activities													111	15	39
CASH FLOWS FROM FINANCING ACTIVITIES
Dividends paid													(4,939)	(4,816)	(4,637)
Issuance of common stock													56	53	39
Purchase of treasury stock													(6)	(94)	(45)
Net cash used in financing activities													(4,889)	(4,857)	(4,643)
Net (decrease) increase in cash													(8)	16	38
CASH
Beginning of year				$ 57				$ 41				$ 3	57	41	3
End of year	$ 49				$ 57				$ 41				49	57	41
Supplemental Disclosures of Cash Flow Information
Interest paid													25	23	31
Dividends paid on Common Stock [Abstract]
Dividends declared													4,949	4,816	4,637
Dividends reinvested													(10)	0	0
Dividends paid on Common Stock													$ 4,939	$ 4,816	$ 4,637