Common Stock and Earnings Per Share (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 03, 2016	Mar. 11, 2013
Common Stock and Earnings Per Share [Abstract]
Net income	$ 3,527	$ 3,931	$ 2,935	$ 2,581	$ 2,942	$ 3,571	$ 2,847	$ 2,486	$ 12,974	$ 11,846	$ 12,489
Shares Used in Computing Basic and Diluted Net Income per Share [Abstract]
Weighted average common shares, basic (in shares)									12,849,123	12,845,955	12,831,687
Effect of dilutive securities [Abstract]
Employee stock-based compensation									48	18	0
Weighted average common shares, diluted (in shares)									12,849,171	12,845,973	12,831,687
Stock Repurchase Program [Abstract]
Number of shares authorized to be repurchased under the stock repurchase program (in shares)													1,200,000
Number of shares repurchased and retired under the stock repurchase program (in shares)									37,229	46,771	121,012
Number of remaining shares authorized to be repurchased under the stock repurchase program (in shares)	618,004								618,004
Employee Stock Purchase Plan [Member]
Common Stock [Abstract]
Minimum period full-time employees must be employed to purchase shares									90 days
Maximum percentage of gross compensation allowed to purchase shares									10.00%
Purchase price as a percentage of fair market value of common stock									95.00%
Number of shares issued (in shares)									4,770	5,115	7,417
Number of authorized shares remaining to be issued (in shares)	70,826								70,826
Dividend Reinvestment and Direct Stock Purchase and Sale Plan [Member]
Common Stock [Abstract]
Number of shares authorized to be issued (in shares)												331,000
Number of shares authorized, unissued, and rolled over under plan												170,240
Number of shares issued (in shares)									51,401	80,343	95,451
Number of authorized shares remaining to be issued (in shares)	441,238								441,238
Optional Dividend Reinvestment Portion of Plan [Member]
Common Stock [Abstract]
Purchase price as a percentage of fair market value of common stock									95.00%
Direct Stock Purchase Portion of Plan [Member]
Common Stock [Abstract]
Purchase price as a percentage of fair market value of common stock									100.00%