Acquisitions (Schedule of Consideration Paid and Net Assets Acquired, Business Acquisitions - Pacer) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 01, 2014	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Identifiable assets acquired and liabilities assumed:
Goodwill		$ 912,885	$ 983,133	$ 1,000,024	$ 1,082,466	$ 902,044	$ 826,600
Earn-Out Arrangements [Member]
Acquisition consideration:
Fair value of contingent consideration (earn-out liability)		$ 8,700	$ 33,612	$ 34,988	$ 33,612	$ 32,451	$ 66,700
Pacer [Member] | Canadian Dollars [Member]
Acquisition consideration:
Cash	$ 126,500
Total consideration transferred	150,800
Identifiable assets acquired and liabilities assumed:
Current assets, including $3.4 million of cash acquired	114,000
Business combinations, cash acquired	3,400
Property and equipment	81,200
Finite-lived intangible assets	19,400
Current liabilities, including current portion of capital lease obligations and long-term debt	(71,800)
Long-term debt, including capital lease obligations	(69,600)
Deferred income taxes	(30,500)
Total identifiable net assets	50,400
Goodwill	100,400
Total net assets acquired, including goodwill	150,800
Pacer [Member] | Canadian Dollars [Member] | Equity Method Investments [Member]
Identifiable assets acquired and liabilities assumed:
Net equity method investment obligations	(31,000)
Pacer [Member] | Canadian Dollars [Member] | Pre-Qualifications [Member]
Identifiable assets acquired and liabilities assumed:
Pre-qualifications	38,700
Pacer [Member] | Canadian Dollars [Member] | Earn-Out Arrangements [Member]
Acquisition consideration:
Fair value of contingent consideration (earn-out liability)	$ 24,300