Risk Management - Risk Concentrations and Interest Rate Risk (Details) (Interest rate swap agreements, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012	Dec. 31, 2011
Interest rate swap agreements
Risk Management-Risk Concentrations and Interest Rate Risk
Number of agreements held	0
Amount of loss recognized in the income statement as an increase in interest expense	$ 1,500	$ 6,400	$ 11,300