Common Stock and Earnings per Share (Schedule of Calculations of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ 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, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic
Net income	$ 6,424	$ 6,222	$ 5,869	$ 5,833	$ 6,089	$ 5,880	$ 5,548	$ 5,539	$ 24,348	$ 23,056	$ 24,033
Weighted average common shares outstanding (in shares)									11,150,395	11,358,609	11,479,025
Basic earnings per share (in dollars per share)	$ 0.58	$ 0.56	$ 0.53	$ 0.52	$ 0.54	$ 0.52	$ 0.49	$ 0.48	$ 2.18	$ 2.03	$ 2.09
Diluted
Net income	$ 6,424	$ 6,222	$ 5,869	$ 5,833	$ 6,089	$ 5,880	$ 5,548	$ 5,539	$ 24,348	$ 23,056	$ 24,033
Weighted average common shares outstanding (in shares)									11,150,395	11,358,609	11,479,025
Effect of dilutive restricted stock, stock options and SARs (in shares)									156,729	159,819	164,954
Weighted average common shares outstanding assuming dilution (in shares)									11,307,124	11,518,428	11,643,979
Diluted earnings per share (in dollars per share)	$ 0.57	$ 0.55	$ 0.52	$ 0.51	$ 0.53	$ 0.51	$ 0.48	$ 0.48	$ 2.15	$ 2.00	$ 2.06