Segment and Geographic Area Information North American, Australian & U.K./European Operations (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) region reportable_segment provinces	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Segment Reporting Information [Line Items]
Number of operating regions | region									11
Number of reportable segments | reportable_segment									3
Freight revenues									$ 1,405,114,000	$ 1,251,941,000	$ 1,177,364,000
Freight-related revenues									497,516,000	290,787,000	287,811,000
All other revenues									97,771,000	96,284,000	103,468,000
OPERATING REVENUES									2,000,401,000	1,639,012,000	1,568,643,000
Income/(loss) from operations	$ 94,631,000	$ 117,559,000	$ 99,451,000	$ 72,620,000	$ 113,471,000	$ 123,116,000	$ 110,109,000	$ 74,875,000	384,261,000	421,571,000	380,188,000
Depreciation and amortization									188,535,000	157,081,000	141,644,000
Loss on settlement of foreign currency forward purchase contracts									18,686,000	1,270,000	2,269,000
Interest expense, net									66,592,000	54,717,000	63,923,000
Provision for/(benefit from) income taxes									75,894,000	107,107,000	46,296,000
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties									$ 329,762,000	303,519,000	215,405,000
North American Operations [Member]
Segment Reporting Information [Line Items]
Number of operating regions | provinces									9
Freight revenues									$ 949,028,000	1,008,236,000	917,971,000
Freight-related revenues									227,154,000	214,388,000	215,302,000
All other revenues									65,633,000	82,137,000	95,899,000
OPERATING REVENUES									1,241,815,000	1,304,761,000	1,229,172,000
Income/(loss) from operations									297,486,000	333,194,000	286,164,000
Depreciation and amortization									141,814,000	127,421,000	113,155,000
Loss on settlement of foreign currency forward purchase contracts									16,374,000
Interest expense, net									39,651,000	41,732,000	48,483,000
Provision for/(benefit from) income taxes									69,552,000	86,363,000	24,446,000
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties									266,548,000	277,725,000	163,157,000
Australian Operations [Member]
Segment Reporting Information [Line Items]
Freight revenues									146,850,000	243,705,000	259,393,000
Freight-related revenues									87,616,000	55,461,000	57,834,000
All other revenues									8,486,000	14,104,000	7,569,000
OPERATING REVENUES									242,952,000	313,270,000	324,796,000
Income/(loss) from operations									54,842,000	90,396,000	95,016,000
Depreciation and amortization									27,425,000	28,095,000	27,102,000
Loss on settlement of foreign currency forward purchase contracts									2,312,000
Interest expense, net									8,976,000	12,152,000	14,814,000
Provision for/(benefit from) income taxes									12,890,000	23,443,000	22,258,000
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties									31,179,000	24,930,000	51,860,000
U.K./European Operations [Member]
Segment Reporting Information [Line Items]
Freight revenues									309,236,000	0	0
Freight-related revenues									182,746,000	20,938,000	14,675,000
All other revenues									23,652,000	43,000	0
OPERATING REVENUES									515,634,000	20,981,000	14,675,000
Income/(loss) from operations									31,933,000	(2,019,000)	(992,000)
Depreciation and amortization									19,296,000	1,565,000	1,387,000
Loss on settlement of foreign currency forward purchase contracts									0
Interest expense, net									17,965,000	833,000	626,000
Provision for/(benefit from) income taxes									(6,548,000)	(2,699,000)	(408,000)
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties									$ 32,035,000	$ 864,000	$ 388,000