Other comprehensive income and credit-risk-related contingent features (Details) (Interest Rate Swaps, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Interest Rate Swaps
Effect of derivative financial instruments on the statements of consolidated operations and statement of consolidated comprehensive income
Amount of gain/(loss) recognized in interest expense for the ineffective portion of derivatives	$ (37)	$ 218	$ (353)
Amount of gain/(loss) recognized in interest expense for derivatives not designated as hedging instruments	$ (4)	$ (54)	$ 484