Operations by Business Segment and Geographic Information Geographic Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment reporting information [Line Items]
Revenues	$ 845,678	$ 821,904	$ 789,911
Long-lived assets, net	245,166	232,652	213,808
United States [Member]
Segment reporting information [Line Items]
Revenues	775,870	749,896	706,145
Long-lived assets, net	224,727	213,323	196,116
Canada [Member]
Segment reporting information [Line Items]
Revenues	69,808	72,008	83,766
Long-lived assets, net	$ 20,439	$ 19,329	$ 17,692