Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income	$ 23,387	$ 19,734	$ 76,079	$ 63,199
Denominator:
Weighted-average shares outstanding - basic (in shares)	18,581,000	18,403,000	18,569,000	18,360,000
Effect of dilutive shares (in shares)	143,000	275,000	146,000	289,000
Weighted-average shares outstanding - dilutive (in shares)	18,724,000	18,678,000	18,715,000	18,649,000
Basic earnings per share (in dollars per share)	$ 1.26	$ 1.07	$ 4.10	$ 3.44
Diluted earnings per share (in dollars per share)	$ 1.25	$ 1.06	$ 4.07	$ 3.39
Anti-dilutive shares excluded (in shares)	3,173	37,700