Acquisitions (Details) (Hill Hire [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Hill Hire [Member]
Summary of purchase price allocations
Revenue earning equipment	$ 200,962
Operating property and equipment	18,780
Customer relationships and other intangibles	10,133
Other assets, primarily accounts receivable	60,179
Assets	290,054
Liabilities, primarily accrued liabilities	(38,559)
Net asset acquired	$ 251,495