Real Estate Mortgages Receivable (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended			12 Months Ended
	Sep. 30, 2013	Jan. 31, 2013 property	Apr. 30, 2012	Dec. 31, 2013	Dec. 31, 2012
Real Estate Mortgages Receivable
Number of properties sold or agreed to be sold		3
Number of buildings sold		18
Mortgage financing related to sale of suburban property		$ 7,688	$ 419	$ 7,688	$ 1,419
Interest rate on real estate mortgage receivable (as a percent)		6.00%	6.00%
Amount received from prepayment of real estate mortgage receivable	1,000
Total real estate mortgage receivable included in other assets, carrying value				$ 8,107	$ 1,419