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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Long-Term Debt - Additional Information (Details)				1 Months Ended	9 Months Ended
Long-Term Debt - Additional Information (Details)	Nov. 03, 2016 USD ($)	Jun. 22, 2016 USD ($)	Dec. 19, 2013 USD ($)	Aug. 31, 2013 USD ($)	Sep. 30, 2017 USD ($)	Mar. 21, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 05, 2014 USD ($)	Mar. 05, 2014 USD ($) investor	Jan. 12, 2012 USD ($)
Debt Instrument [Line Items]
Weighted average interest rate (as a percent)					2.89%
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						$ 1,563,239,000
Senior Notes Due 2026
Debt Instrument [Line Items]
Stated interest rate (as a percent)					3.45%		3.45%
Long-term debt					$ 747,590,000		$ 747,474,000
4.375% Senior Notes, due 2023
Debt Instrument [Line Items]
Stated interest rate (as a percent)					4.375%		4.375%
Long-term debt					$ 248,502,000		$ 248,310,000
2016 Refinancing Credit Agreement
Debt Instrument [Line Items]
Deferred financing cost		$ 3,300,000
Minimum interest expense coverage ratio					3.0
Maximum debt to EBITDA 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 \| 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					$ 35,400,000
2013 Refinancing Credit Agreement
Debt Instrument [Line Items]
Deferred financing cost			$ 1,000,000
Debt instrument, basis spread on variable rate					1.00%
Basis spread on effective rate					0.50%
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%
Schuldschein Loan
Debt Instrument [Line Items]
Long-term debt					$ 11,812,000		98,671,000
Schuldschein Loan \| Faiveley Transport
Debt Instrument [Line Items]
Stated interest rate (as a percent)					4.00%
Acquired loans									$ 137,200,000
Number of investors \| investor									20
Repayments of debt					$ 125,800,000
Long-term debt					$ 11,800,000
Schuldschein Loan \| March 2021 \| Faiveley Transport
Debt Instrument [Line Items]
Original maturities					7 years
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 rate (as a percent)	3.45%
Deferred financing cost	$ 2,700,000
Long-term debt					$ 747,590,000		747,474,000
Senior Notes \| 4.375% Senior Notes, due 2023
Debt Instrument [Line Items]
Debt issued				$ 250,000,000
Debt issuance price (as a percent)				99.879%
Stated interest rate (as a percent)				4.375%
Deferred financing cost				$ 2,600,000
Long-term debt					248,502,000		248,310,000
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt					855,321,000		$ 796,150,000
Line of Credit \| 2016 Refinancing Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, amount		$ 1,200,000,000.0
Credit facility loan term, years		5 years
Line of credit facility, amount currently available					$ 686,700,000
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
Credit facility loan term, years			5 years