Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Details) (Interest rate swaps, Recurring Measurements, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets and liabilities that are measured at fair value on a recurring basis
Interest rate swap assets/(liabilities)	$ (1,619)	$ 0
Level 1
Assets and liabilities that are measured at fair value on a recurring basis
Interest rate swap assets/(liabilities)	0	0
Level 2
Assets and liabilities that are measured at fair value on a recurring basis
Interest rate swap assets/(liabilities)	(1,619)	0
Level 3
Assets and liabilities that are measured at fair value on a recurring basis
Interest rate swap assets/(liabilities)	$ 0	$ 0