Derivative Financial Instruments Foreign Currency Exchange Rate Risk (Details) £ in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2015 GBP (£)	Mar. 31, 2015 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 GBP (£)	Jun. 30, 2018 USD ($)	Mar. 25, 2015 GBP (£)	Mar. 25, 2015 USD ($)
Derivative [Line Items]
Foreign subsidiaries third-party debt denominated in local currencies | $								$ 1,100,000
Foreign Currency Forward [Member]
Derivative [Line Items]
Existing net gains expected to be realized within the next 12 months | $					$ 400
Foreign Currency Forward 1 [Member]
Derivative [Line Items]
Effective Date					Apr. 18, 2018
Settlement Date					Jul. 05, 2018
Notional Amount | $								$ 5,379
Exchange Rate							0.78	0.78
Foreign Currency Forward 2 [Member]
Derivative [Line Items]
Effective Date					May 02, 2018
Settlement Date					Nov. 05, 2018
Notional Amount | $								$ 4,315
Exchange Rate							0.75	0.75
Foreign Currency Forward 3 [Member]
Derivative [Line Items]
Effective Date					May 02, 2018
Settlement Date					Dec. 21, 2018
Notional Amount | $								$ 5,753
Exchange Rate							0.75	0.75
British Pound Foreign currency forward contracts [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion | $	$ 200	$ 100			$ 300	$ 300
Existing net gains expected to be realized within the next 12 months | $					$ 700
British Pound Foreign Currency Forward Contract 1 [Member]
Derivative [Line Items]
Effective Date					Mar. 25, 2015
Settlement Date					Mar. 31, 2020
Notional Amount							£ 60,000
Exchange Rate							1.51	1.51
British Pound Foreign Currency Forward Contract 2 [Member]
Derivative [Line Items]
Effective Date					Mar. 25, 2015
Settlement Date					Mar. 31, 2020
Notional Amount							£ 60,000
Exchange Rate							1.50	1.50
British Pound Foreign Currency Forward Contract 3 [Member]
Derivative [Line Items]
Effective Date					Jun. 30, 2015
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,035
Exchange Rate							1.57	1.57
British Pound Foreign Currency Forward Contract 4 [Member]
Derivative [Line Items]
Effective Date					Sep. 30, 2015
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,846
Exchange Rate							1.51	1.51
British Pound Foreign Currency Forward Contract 5 [Member]
Derivative [Line Items]
Effective Date					Dec. 31, 2015
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,873
Exchange Rate							1.48	1.48
British Pound Foreign Currency Forward Contract 6 [Member]
Derivative [Line Items]
Effective Date					Mar. 31, 2016
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,881
Exchange Rate							1.45	1.45
British Pound Foreign Currency Forward Contract 7 [Member]
Derivative [Line Items]
Effective Date					Jun. 30, 2016
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,909
Exchange Rate							1.35	1.35
British Pound Foreign Currency Forward Contract 8 [Member]
Derivative [Line Items]
Effective Date					Sep. 30, 2016
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,959
Exchange Rate							1.33	1.33
British Pound Foreign Currency Forward Contract 9 [Member]
Derivative [Line Items]
Effective Date					Dec. 30, 2016
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,989
Exchange Rate							1.28	1.28
British Pound Foreign Currency Forward Contract 10 [Member]
Derivative [Line Items]
Effective Date					Mar. 31, 2017
Settlement Date					Mar. 31, 2020
Notional Amount							£ 1,975
Exchange Rate							1.30	1.30
British Pound Foreign Currency Forward Contract 11 [Member]
Derivative [Line Items]
Effective Date					Jun. 30, 2017
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,026
Exchange Rate							1.34	1.34
British Pound Foreign Currency Forward Contract 12 [Member]
Derivative [Line Items]
Effective Date					Oct. 02, 2017
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,079
Exchange Rate							1.36	1.36
British Pound Foreign Currency Forward Contract 13 [Member]
Derivative [Line Items]
Effective Date					Dec. 29, 2017
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,111
Exchange Rate							1.39	1.39
British Pound Foreign Currency Forward Contract 14 [Member]
Derivative [Line Items]
Effective Date					Mar. 31, 2018
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,096
Exchange Rate							1.44	1.44
British Pound Foreign Currency Forward Contract 15 [Member]
Derivative [Line Items]
Effective Date					Jun. 29, 2018
Settlement Date					Mar. 31, 2020
Notional Amount							£ 2,151
Exchange Rate							1.36	1.36
Freightliner [Member]
Derivative [Line Items]
Cash consideration			£ 492,100	$ 733,000
Intercompany Loan [Member]
Derivative [Line Items]
Long-term Debt, Gross									£ 120,000	$ 181,000
Accrued interest							£ 25,900	$ 34,200