Fair Value of Financial Instruments Financial Instruments Carried at Fair Value(Details) £ in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016 USD ($)	Dec. 31, 2016 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		$ (2,300)
Freightliner [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of economic interest retained by acquiree's management	6.00%
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial assets carried at fair value				$ 27,039		$ 1,530
Financial Liabilities Fair Value Disclosure				15,175		12,501
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Business Combination, Contingent Consideration, Liability			£ 25,882	31,933	£ 24,200	35,680
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liability				15,158		12,501
British pound forward contracts [Member] | Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset				26,359		1,530
Derivative Liability				17		0
Currency Swap [Member] | Not Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset				$ 680		$ 0