Earnings Per Share (Calculation of Basic and Diluted EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 23,543	$ 16,592	$ 56,897	$ 41,075
Average Common Shares:
Basic (weighted-average outstanding shares)	11,689	11,586	11,649	11,535
Dilutive potential common shares from stock options (in shares)	88	122	109	131
Diluted (weighted-average outstanding shares)	11,777	11,708	11,758	11,666
Basic earnings per share (in dollars per share)	$ 2.01	$ 1.43	$ 4.88	$ 3.56
Diluted earnings per share (in dollars per share)	$ 2.00	$ 1.42	$ 4.84	$ 3.52