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Long-Term Debt - Additional Information (Details)					3 Months Ended
Long-Term Debt - Additional Information (Details)	Mar. 06, 2017 USD ($)	Oct. 31, 2016 USD ($)	Jun. 22, 2016 USD ($)	Dec. 19, 2013 USD ($)	Mar. 31, 2017 USD ($) tranche	Dec. 31, 2016 USD ($)	Jun. 05, 2014 USD ($)	Mar. 05, 2014 USD ($) investor	Aug. 31, 2013 USD ($)	Jan. 12, 2012 USD ($)
Debt Instrument [Line Items]
Repayments of debt	$ 39,600,000				$ 18,700,000
Weighted average interest rate (as a percent)					2.61%
Forward Starting Interest Rate Swap Agreement
Debt Instrument [Line Items]
Interest rate swap agreements, notional amount							$ 150,000,000			$ 150,000,000.0
Interest rate on notional value (as a percent)							2.56%			1.415%
Faiveley Transport
Debt Instrument [Line Items]
Acquired loans					$ 1,531,999,000
Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt					825,773,000	$ 796,150,000
Unamortized discount and debt issuance cost					$ 3,500,000	$ 3,850,000
Senior Notes Due 2026
Debt Instrument [Line Items]
Stated interest percentage					3.45%	3.45%
Long-term debt					$ 747,515,000	$ 747,474,000
Unamortized discount and debt issuance cost					$ 2,485,000	$ 2,526,000
2016 Refinancing Credit Agreement
Debt Instrument [Line Items]
Deferred financing cost			$ 3,300,000
Minimum interest expense coverage ratio					3.0
Maximum debt to cash flow ratio					3.25
2016 Refinancing Credit Agreement \| Federal Funds Effective Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.50%
2016 Refinancing Credit Agreement \| LIBOR Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					1.00%
2016 Refinancing Credit Agreement \| Base Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.00%
2016 Refinancing Credit Agreement \| Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.00%
2016 Refinancing Credit Agreement \| Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.75%
2016 Refinancing Credit Agreement \| Alternative Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					1.75%
2016 Refinancing Credit Agreement \| Alternative Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.75%
2016 Refinancing Credit Agreement \| Alternative Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					1.75%
2016 Refinancing Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility loan term, years			5 years
Line of credit facility, amount currently available					$ 728,000,000
2016 Refinancing Credit Agreement \| Term Loan
Debt Instrument [Line Items]
Ticking fee			0.10%
2016 Refinancing Credit Agreement \| Letter of Credit
Debt Instrument [Line Items]
Line of credit amount outstanding					$ 32,700,000
4.375% Senior Notes, due 2023
Debt Instrument [Line Items]
Stated interest percentage					4.375%	4.375%
Long-term debt					$ 248,374,000	$ 248,310,000
Unamortized discount and debt issuance cost					$ 1,626,000	1,690,000
2013 Refinancing Credit Agreement
Debt Instrument [Line Items]
Deferred financing cost				$ 1,000,000
Basis spread on effective rate					0.50%
Debt instrument, basis spread on variable rate					1.00%
2013 Refinancing Credit Agreement \| Base Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.00%
2013 Refinancing Credit Agreement \| Base Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.75%
2013 Refinancing Credit Agreement \| Alternative Rate \| Minimum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					0.75%
2013 Refinancing Credit Agreement \| Alternative Rate \| Maximum
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate					1.75%
2013 Refinancing Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility loan term, years				5 years
Schuldschein Loan
Debt Instrument [Line Items]
Long-term debt					$ 41,718,000	$ 98,671,000
Schuldschein Loan \| Faiveley Transport
Debt Instrument [Line Items]
Long-term debt					41,700,000
Acquired loans								$ 137,200,000
Number of investors \| investor								20
Repayments of debt					$ 95,500,000
Number of loan tranches \| tranche					3
Senior Notes \| Senior Notes Due 2026
Debt Instrument [Line Items]
Debt issued		$ 750,000,000
Debt issuance price (as a percent)		99.965%
Stated interest percentage		3.45%
Deferred financing cost		$ 2,600,000
Line of Credit \| 2016 Refinancing Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, amount			$ 1,200,000,000.0
Line of Credit \| 2016 Refinancing Credit Agreement \| Term Loan
Debt Instrument [Line Items]
Revolving credit facility, amount			$ 400,000,000.0
Line of Credit \| 2013 Refinancing Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, amount				$ 800,000,000
4.375% Senior Notes, due 2023
Debt Instrument [Line Items]
Stated interest percentage									4.375%
Deferred financing cost									$ 2,600,000
Long-term debt									$ 250,000,000
Senior notes coupon rate									99.879%
Five Year Maturity \| Schuldschein Loan
Debt Instrument [Line Items]
Stated interest percentage					3.04%
Long-term debt					$ 21,390,000
Seven Year Maturity \| Schuldschein Loan
Debt Instrument [Line Items]
Stated interest percentage					3.07%
Long-term debt					$ 9,630,000
Seven Year Maturity \| Schuldschein Loan \| Faiveley Transport
Debt Instrument [Line Items]
Original maturities					7 years
Ten Year Maturity \| Schuldschein Loan
Debt Instrument [Line Items]
Stated interest percentage					4.00%
Long-term debt					$ 10,698,000
Ten Year Maturity \| Schuldschein Loan \| Faiveley Transport
Debt Instrument [Line Items]
Original maturities					10 years