Segment Information (Schedule of Revenue by Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues	$ 175,244	$ 190,441	$ 163,229	$ 149,681	$ 155,681	$ 174,027	$ 141,495	$ 127,896	$ 678,595	$ 599,099	$ 575,336
United States
Revenues									676,956	597,899	573,398
Canada
Revenues									481	173	851
Mexico
Revenues									$ 1,158	$ 1,027	919
Other
Revenues											$ 168