Acquisitions - Pacer International - Additional Information (Detail) $ / shares in Units, $ in Millions	Mar. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2015 $ / shares	Sep. 08, 2015 $ / shares	Dec. 31, 2014 $ / shares
Business Acquisition [Line Items]
Common stock, par value (in usd per share)		$ 0.001	$ 0.001	$ 0.001
Pacer International
Business Acquisition [Line Items]
Common stock, par value (in usd per share)	$ 0.01
Right to receive price per share (in usd per share)	$ 6.00
Exchange ratio per share	0.1017
Base line share price (in usd per share)	$ 3.00
Payment period of purchase consideration	10 days
Total consideration paid | $	$ 331.5
Cash consideration | $	223.3
Business acquisition, equity interest issued or issuable | $	$ 108.2
Business acquisition, equity interest issued or issuable, number of shares | shares	3,688,246
Common stock price per share (in usd per share)	$ 29.41
Total tax deductible goodwill | $	$ 323.2