Segments - Sales by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues by geographic areas	$ 604,973	$ 529,230	$ 1,141,270	$ 1,008,687
United States
Segment Reporting Information [Line Items]
Revenues by geographic areas	537,819	470,079	1,010,760	897,020
Canada
Segment Reporting Information [Line Items]
Revenues by geographic areas	$ 67,154	$ 59,151	$ 130,510	$ 111,667