Earnings Per Common Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Common Share (EPS) [Abstract]
Net income	$ 23,584	$ 28,801	$ 67,444	$ 65,561
Weighted-average common shares outstanding - basic	49,775	49,185	49,602	49,132
Effect of dilutive restricted stock units and stock options	812	915	1,166	517
Weighted-average common shares outstanding - diluted	50,587	50,100	50,768	49,649
Net income per share: Basic	$ 0.47	$ 0.59	$ 1.36	$ 1.33
Net income per share: Diluted	$ 0.47	$ 0.57	$ 1.33	$ 1.32
Anti-dilutive shares not included above	912	610	752	1,339