Derivative Financial Instruments Foreign Currency Exchange Rate Risk (Details) £ in Thousands, $ in Thousands, AUD in Millions			3 Months Ended		12 Months Ended
	Feb. 25, 2015 GBP (£)	Feb. 25, 2015 USD ($)	Mar. 31, 2015 GBP (£)	Mar. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 USD ($)	Mar. 25, 2015 GBP (£)	Mar. 25, 2015 USD ($)	Mar. 23, 2015 GBP (£)	Feb. 25, 2015 AUD	Feb. 25, 2015 GBP (£)	Feb. 25, 2015 USD ($)
Derivatives [Line Items]
Third party debt related to foreign operations denominated in foreign currencies									$ 1,100,000
Cash received on settlement of forward currency forward purchase contracts | £												£ 391,800
Loss on settlement of foreign currency forward purchase contracts					$ 0	$ 0	$ (18,686)
Foreign currency forward purchase contract 1 [Member]
Derivatives [Line Items]
Notional Amount														£ 307,100	$ 475,000
Foreign currency forward purchase contract 2 [Member]
Derivatives [Line Items]
Notional Amount													AUD 163.8	£ 84,700
Forward Contracts [Member]
Derivatives [Line Items]
Loss on settlement of foreign currency forward purchase contracts						18,700
Foreign Exchange Forward [Member]
Derivatives [Line Items]
Gain/(loss) reclassified from accumulated other comprehensive income/(loss) into earnings due to ineffectiveness					0	0	0
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					600	$ 800
Existing net gains expected to be realized within the next 12 months					$ 600
Freightliner [Member]
Derivatives [Line Items]
Loss on settlement of foreign currency forward purchase contracts							$ (18,700)
Cash consideration			£ 492,083	$ 733,006
Intercompany Loan [Member]
Derivatives [Line Items]
Long-term Debt, Gross										£ 120,000	$ 181,000
Accumulated accrued interest								£ 21,700	$ 29,300
Scenario, Plan [Member] | Freightliner [Member]
Derivatives [Line Items]
Estimated Payments to Acquire Businesses, Gross	£ 490,000	$ 755,000