Segment Information Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) reportable_segment region	Jun. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of operating regions | region			10
Number of reportable segments | reportable_segment			3
Restructuring costs	$ 4,970	$ 0	$ 6,097	$ 0
Freight revenues	340,782	374,615	667,196	672,824
Freight-related revenues	133,688	137,891	267,146	216,016
All other revenues	26,905	29,713	49,649	50,409
Total Operating revenues	501,375	542,219	983,991	939,249
Operating income/(loss)	87,194	99,451	144,190	172,071
Depreciation and amortization	50,924	48,048	100,254	90,265
Interest expense, net	17,405	17,648	35,305	31,130
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	0	0	0	18,686
Provision for/(benefit from) income taxes	22,112	29,300	34,920	46,162
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	55,648	87,627	87,331	137,525
North American Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			700
Freight revenues	227,082	238,153	448,907	481,183
Freight-related revenues	60,978	55,589	122,503	113,650
All other revenues	16,515	17,238	32,943	33,771
Total Operating revenues	304,575	310,980	604,353	628,604
Operating income/(loss)	79,023	76,621	149,001	133,702
Depreciation and amortization	37,124	34,936	73,313	70,241
Interest expense, net	9,666	9,588	20,130	20,361
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				16,374
Provision for/(benefit from) income taxes	20,953	24,939	36,962	39,226
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	39,523	73,440	64,939	118,710
Australian Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			700
Freight revenues	26,394	39,464	51,171	85,822
Freight-related revenues	27,129	25,173	52,619	36,037
All other revenues	1,760	2,171	3,291	4,891
Total Operating revenues	55,283	66,808	107,081	126,750
Operating income/(loss)	9,381	15,131	(2,370)	29,367
Depreciation and amortization	7,233	7,394	13,889	13,620
Interest expense, net	2,398	2,271	4,793	4,604
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				2,312
Provision for/(benefit from) income taxes	2,247	3,829	(277)	6,757
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	4,787	9,159	5,654	13,774
U.K./European Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			4,700
Freight revenues	87,306	96,998	167,118	105,819
Freight-related revenues	45,581	57,129	92,024	66,329
All other revenues	8,630	10,304	13,415	11,747
Total Operating revenues	141,517	164,431	272,557	183,895
Operating income/(loss)	(1,210)	7,699	(2,441)	9,002
Depreciation and amortization	6,567	5,718	13,052	6,404
Interest expense, net	5,341	5,789	10,382	6,165
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				0
Provision for/(benefit from) income taxes	(1,088)	532	(1,765)	179
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	$ 11,338	$ 5,028	$ 16,738	$ 5,041