Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income	$ 12,455	$ 20,388	$ 39,621	$ 45,870
Denominator:
Weighted-average shares outstanding - basic (shares)	18,430,000	18,259,000	18,511,000	18,123,000
Effect of dilutive stock options (shares)	220,000	475,000	374,000	534,000
Weighted-average shares outstanding - diluted (shares)	18,650,000	18,734,000	18,885,000	18,657,000
Basic earnings per share (in dollars per share)	$ 0.68	$ 1.12	$ 2.14	$ 2.53
Diluted earnings per share (in dollars per share)	$ 0.67	$ 1.09	$ 2.10	$ 2.46
Anti-dilutive shares excluded (shares)	14,000	22,350