Other Assets - Narrative (Details) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended					9 Months Ended
	Jan. 31, 2013 building property	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 property building	Jun. 30, 2013 building property	Sep. 30, 2012 building property	Jun. 30, 2012 property building	Apr. 30, 2012 property building	Sep. 30, 2013	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total real estate mortgage receivable included in other assets, carrying value		$ 8,100,000		8,100,000						$ 8,107,000
Mortgage financing related to property sold		7,688,000	1,419,000
Number of properties sold or agreed to be sold	3
Number of buildings	18
Real estate mortgages receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for losses related to real estate mortgages receivable		0		0						0
Sales of properties resulting in gains and losses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties sold or agreed to be sold		7	3
Number of buildings		59	0
Sales of properties resulting in gains and losses | Suburban office and industrial properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage financing related to property sold	7,700,000
Interest rate on real estate mortgage receivable	6.00%
Number of properties sold or agreed to be sold	3
Number of buildings	18
Sales of properties resulting in gains and losses | Suburban property
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage financing related to property sold								$ 400,000	$ 1,000,000
Interest rate on real estate mortgage receivable							5.00%	6.00%
Number of properties sold or agreed to be sold				3	1	1	1	1
Number of buildings				40	1	0	0	0