Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 Recurring basis Level 2	Dec. 31, 2012 Recurring basis Level 2	Mar. 31, 2013 Nonrecurring basis Level 3	Mar. 31, 2012 Nonrecurring basis Level 3
Fair value measurements
Interest rate swaps liability	$ (8,727)	$ (9,916)
Impaired long-lived assets			$ 453	$ 359