Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income	$ 26,136	$ 27,032
Denominator:
Weighted-average shares outstanding - basic (shares)	18,288,000	18,056,000
Effect of dilutive shares (shares)	322,000	317,000
Weighted-average shares outstanding - diluted (shares)	18,610,000	18,373,000
Basic earnings per share (in dollars per share)	$ 1.43	$ 1.50
Diluted earnings per share (in dollars per share)	$ 1.40	$ 1.47
Anti-dilutive shares excluded (shares)	0