Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Common Share (EPS) [Abstract]
Net income	$ 30,096	$ 21,361	$ 43,860	$ 36,760
Weighted-average common shares outstanding - basic	49,735	49,131	49,510	49,105
Effect of dilutive restricted stock units and stock options	1,020	430	1,343	318
Weighted-average common shares outstanding - diluted	50,755	49,561	50,853	49,423
Net income per share: Basic	$ 0.61	$ 0.43	$ 0.89	$ 0.75
Net income per share: Diluted	$ 0.59	$ 0.43	$ 0.86	$ 0.74
Anti-dilutive shares not included above	353	1,704	672	1,704