Fair Value of Financial Instruments Financial instruments Carried at Fair Value-Level 3 (Details) £ in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016 GBP (£)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 USD ($)
Freightliner [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Percentage of economic interest retained by acquiree's management	6.00%
Liability [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial Liabilities carried at fair value, Other Liabilities deferred consideration		£ 24,266	$ 34,926	£ 24,200	$ 35,680