Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 161,826	$ 129,559	$ 143,990
Income taxes paid	22,965	13,692	14,062
Changes in accounts payable related to purchases of revenue earning equipment	114,862	80,781	(142,256)
Operating and revenue earning equipment acquired under capital leases	$ 10,701	$ 7,057	$ 1,230