Segment Information Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) reportable_segment region	Sep. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of operating regions | region			10
Number of reportable segments | reportable_segment			3
Restructuring costs	$ 223	$ 0	$ 6,320	$ 0
Freight revenues	349,807	378,936	1,017,003	1,051,760
Freight-related revenues	129,520	145,508	396,666	361,524
All other revenues	21,675	21,855	71,324	72,264
Total Operating revenues	501,002	546,299	1,484,993	1,485,548
Operating income/(loss)	91,851	117,559	236,041	289,630
Depreciation and amortization	50,841	48,303	151,095	138,568
Interest expense, net	16,917	17,239	52,222	48,369
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments	0	0	0	18,686
Provision for/(benefit from) income taxes	19,643	36,855	54,563	83,017
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	42,240	107,169	129,571	244,694
North American Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			800
Freight revenues	232,247	241,410	681,154	722,593
Freight-related revenues	62,124	56,823	184,627	170,473
All other revenues	15,823	16,330	48,766	50,101
Total Operating revenues	310,194	314,563	914,547	943,167
Operating income/(loss)	87,153	90,564	236,154	224,266
Depreciation and amortization	37,085	35,158	110,398	105,399
Interest expense, net	9,600	9,788	29,730	30,149
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				16,374
Provision for/(benefit from) income taxes	22,392	32,333	59,354	71,559
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	30,343	86,620	95,282	205,330
Australian Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			800
Freight revenues	29,219	32,780	80,390	118,602
Freight-related revenues	23,523	26,206	76,142	62,243
All other revenues	1,408	2,027	4,699	6,918
Total Operating revenues	54,150	61,013	161,231	187,763
Operating income/(loss)	4,372	14,966	2,002	44,333
Depreciation and amortization	7,129	7,151	21,018	20,771
Interest expense, net	2,170	2,055	6,963	6,659
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				2,312
Provision for/(benefit from) income taxes	798	3,896	521	10,653
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	2,440	6,354	8,094	20,128
U.K./European Operations [Member]
Segment Reporting Information [Line Items]
Restructuring costs			4,700
Freight revenues	88,341	104,746	255,459	210,565
Freight-related revenues	43,873	62,479	135,897	128,808
All other revenues	4,444	3,498	17,859	15,245
Total Operating revenues	136,658	170,723	409,215	354,618
Operating income/(loss)	326	12,029	(2,115)	21,031
Depreciation and amortization	6,627	5,994	19,679	12,398
Interest expense, net	5,147	5,396	15,529	11,561
Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments				0
Provision for/(benefit from) income taxes	(3,547)	626	(5,312)	805
Expenditures for Additions to Property and Equipment Net of Grants From Outside Parties	$ 9,457	$ 14,195	$ 26,195	$ 19,236