Earnings Per Share (Computation of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income	$ 20,896	$ 5,377	$ 47,928	$ 20,305
Denominator:
Weighted-average shares outstanding - basic (shares)	18,140,000	18,007,000	18,098,000	17,986,000
Effect of dilutive shares (shares)	407,000	246,000	362,000	248,000
Weighted-average shares outstanding - diluted (shares)	18,547,000	18,253,000	18,460,000	18,234,000
Basic earnings per share (in dollars per share)	$ 1.15	$ 0.30	$ 2.65	$ 1.13
Diluted earnings per share (in dollars per share)	$ 1.13	$ 0.29	$ 2.60	$ 1.11
Anti-dilutive shares excluded (shares)	0	13,500