Earnings Per Share (Calculation of Basic and Diluted EPS) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 11,384	$ 14,756	$ 9,710	$ 7,359	$ 11,351	$ 13,367	$ 9,195	$ 7,238	$ 43,209	$ 41,151	$ 36,094
Average common shares:
Basic (weighted-average outstanding shares)									11,349,000	11,875,000	12,050,000
Dilutive potential common shares from stock options, shares									133,000	164,000	162,000
Diluted (weighted-average outstanding shares)	11,500,000	11,496,000	11,498,000	11,436,000	11,403,000	12,205,000	12,276,000	12,270,000	11,482,000	12,039,000	12,212,000
Basic earnings per share (in dollars per share)									$ 3.81	$ 3.47	$ 3.00
Diluted earnings per share (in dollars per share)	$ 0.99	$ 1.28	$ 0.84	$ 0.64	$ 1.00	$ 1.10	$ 0.75	$ 0.59	$ 3.76	$ 3.42	$ 2.96
Stock options excluded from diluted earnings per share calculation (shares)									61,690	37,261	3,831