Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Jun. 30, 2013 Significant Other Observable Inputs (Level 2) Recurring basis	Dec. 31, 2012 Significant Other Observable Inputs (Level 2) Recurring basis	Jun. 30, 2013 Significant Unobservable Inputs (Level 3) Nonrecurring basis	Jun. 30, 2012 Significant Unobservable Inputs (Level 3) Nonrecurring basis
Summarizes the valuation of interest rate swaps and impaired assets
Interest rate swaps asset		$ 132
Interest rate swaps liability		(3,276)	(9,916)
Impaired long-lived assets				3,825	31,605
Impaired long-lived assets-Discontinued operations					$ 22,035
Disposition of impaired fleet assets minimum time required	12 months
Weighted average disposal period of impaired fleet assets	4 years
Weighted average discount rate of expected proceeds on impaired fleet assets (as a percent)	10.40%