Derivatives (Details 1) (Forward starting interest rate swaps (1) [Member], Other assets/Other liabilities [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Forward starting interest rate swaps (1) [Member] | Other assets/Other liabilities [Member]
Summary of types of derivatives by their locations within statements of operations and Financial Position
Asset Derivatives	$ 0	$ 0
Liability Derivatives	$ 4,085	$ 1,596