Segment and Geographic Area Information North American, Australian & U.K./European Operations (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / AUD	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) region reportable_segment	Dec. 31, 2016 USD ($) region $ / AUD	Dec. 31, 2015 USD ($) $ / AUD	Dec. 31, 2017 $ / AUD	Dec. 31, 2017 $ / £	Dec. 31, 2017 $ / CAD	Dec. 31, 2017 $ / €	May 03, 2017 $ / AUD	Dec. 31, 2016 $ / £	Dec. 31, 2016 $ / CAD	Dec. 31, 2016 $ / €	Dec. 31, 2015 $ / £	Dec. 31, 2015 $ / CAD	Dec. 31, 2015 $ / €	Mar. 25, 2015 $ / £
Segment Reporting Information [Line Items]
Number of operating regions | region									9	10
Number of reportable segments | reportable_segment									3
Noncontrolling Interest, Ownership Percentage by Parent	51.10%								51.10%
Restructuring costs									$ 10,160,000	$ 8,182,000	$ 0
Foreign Currency Exchange Rate, Translation					0.74					0.74	0.75					1.29				1.51			1.49
Freight revenues									1,553,875,000	$ 1,371,566,000	$ 1,400,547,000
Freight-related revenues									533,651,000	536,359,000	502,083,000
All other revenues									120,518,000	93,602,000	97,771,000
Operating revenues									2,208,044,000	2,001,527,000	2,000,401,000
Operating income/(loss)	$ 108,179,000	$ 111,489,000	$ 101,340,000	$ 77,454,000	$ 53,571,000	$ 91,851,000	$ 87,194,000	$ 56,996,000	398,462,000	289,612,000	384,261,000
Depreciation and amortization									250,457,000	205,188,000	188,535,000
Interest expense, net									105,209,000	74,534,000	66,592,000
Provision for/(benefit from) income taxes									(261,259,000)	74,395,000	75,894,000
Cash expenditures for additions to property & equipment, net of grants from outside parties									208,223,000	183,450,000	329,762,000
Loss on settlement of foreign currency forward purchase contracts									$ 0	0	18,686,000
North American Operations [Member]
Segment Reporting Information [Line Items]
Number of operating regions | region									7
Restructuring costs									$ 500,000	900,000
Freight revenues									961,356,000	913,619,000	949,028,000
Freight-related revenues									249,623,000	258,922,000	227,154,000
All other revenues									63,306,000	64,223,000	65,633,000
Operating revenues									1,274,285,000	1,236,764,000	1,241,815,000
Operating income/(loss)									303,882,000	319,551,000	297,486,000
Depreciation and amortization									158,006,000	147,527,000	141,814,000
Interest expense, net									38,547,000	40,985,000	39,651,000
Provision for/(benefit from) income taxes									(266,063,000)	80,701,000	69,552,000
Cash expenditures for additions to property & equipment, net of grants from outside parties									166,685,000	137,334,000	266,548,000
Loss on settlement of foreign currency forward purchase contracts											16,374,000
Australian Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs									300,000	800,000
Freight revenues									254,653,000	120,622,000	146,850,000
Freight-related revenues									46,696,000	95,776,000	87,616,000
All other revenues									6,161,000	6,188,000	8,486,000
Operating revenues									307,510,000	222,586,000	242,952,000
Operating income/(loss)									77,251,000	4,810,000	54,842,000
Depreciation and amortization									61,142,000	30,863,000	27,425,000
Interest expense, net									54,718,000	13,958,000	8,976,000
Provision for/(benefit from) income taxes									6,110,000	988,000	12,890,000
Cash expenditures for additions to property & equipment, net of grants from outside parties									16,076,000	11,285,000	31,179,000
Loss on settlement of foreign currency forward purchase contracts											2,312,000
U.K./European Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs									9,400,000	6,500,000
Freight revenues									337,866,000	337,325,000	304,669,000
Freight-related revenues									237,332,000	181,661,000	187,313,000
All other revenues									51,051,000	23,191,000	23,652,000
Operating revenues									626,249,000	542,177,000	515,634,000
Operating income/(loss)									17,329,000	(34,749,000)	31,933,000
Depreciation and amortization									31,309,000	26,798,000	19,296,000
Interest expense, net									11,944,000	19,591,000	17,965,000
Provision for/(benefit from) income taxes									(1,306,000)	(7,294,000)	(6,548,000)
Cash expenditures for additions to property & equipment, net of grants from outside parties									$ 25,462,000	$ 34,831,000	32,035,000
Loss on settlement of foreign currency forward purchase contracts											$ 0
Last day rate [Member]
Segment Reporting Information [Line Items]
Foreign Currency Exchange Rate, Translation					0.72					0.72		0.78	1.35	0.80	1.20		1.23	0.74	1.06
Year to Date Average [Member]
Segment Reporting Information [Line Items]
Foreign Currency Exchange Rate, Translation					0.74					0.74	0.75	0.77	1.29	0.77	1.13		1.36	0.76	1.11	1.53	0.78	1.11
MIRA [Member]
Segment Reporting Information [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	48.90%								48.90%