Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income	$ 24,293	$ 17,329	$ 52,692	$ 43,465
Denominator:
Weighted-average shares outstanding - basic (in shares)	18,568,000	18,389,000	18,562,000	18,338,000
Effect of dilutive shares (in shares)	162,000	271,000	149,000	297,000
Weighted-average shares outstanding - dilutive (in shares)	18,730,000	18,660,000	18,711,000	18,635,000
Basic earnings per share (in dollars per share)	$ 1.31	$ 0.94	$ 2.84	$ 2.37
Diluted earnings per share (in dollars per share)	$ 1.30	$ 0.93	$ 2.82	$ 2.33
Anti-dilutive shares excluded (in shares)	6,256	27,145