Real Estate Mortgages Receivable - Narrative (Details)	1 Months Ended
	Jan. 31, 2013 USD ($) property building	Apr. 30, 2012 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Real Estate Mortgages Receivable
Total real estate mortgage receivable included in other assets, carrying value			$ 8,100,000	$ 8,100,000
Mortgage financing related to sale of suburban property	$ 7,700,000	$ 400,000
Interest rate on real estate mortgage receivable	6.00%	6.00%
Number of properties sold or agreed to be sold | property	3
Number of Buildings | building	18
Allowance for mortgage receivables			$ 0	$ 0