Segmented Information (Geographic Information of Revenue) (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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 178,785	$ 141,047	$ 166,186	$ 124,499	$ 146,769	$ 128,876	$ 158,805	$ 131,945	$ 135,462	$ 109,318	$ 155,477	$ 115,618	$ 610,517	$ 566,395	$ 515,875
Operating Segments [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													610,517	566,395	515,875
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													325,244	278,198	257,824
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													168,928	187,699	166,528
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													68,408	52,809	48,419
Other [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													$ 47,937	$ 47,689	$ 43,104