Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income	$ 7,006	$ 23,387	$ 34,785	$ 76,079
Denominator:
Weighted-average shares outstanding - basic (in shares)	18,688,000	18,581,000	18,678,000	18,569,000
Effect of dilutive shares (in shares)	25,000	143,000	17,000	146,000
Weighted-average shares outstanding - dilutive (in shares)	18,713,000	18,724,000	18,695,000	18,715,000
Basic earnings per share (in dollars per share)	$ 0.37	$ 1.26	$ 1.86	$ 4.10
Diluted earnings per share (in dollars per share)	$ 0.37	$ 1.25	$ 1.86	$ 4.07
Anti-dilutive shares excluded (in shares)	32,501	3,173