Investments in Partnerships - Apartment Communities Owned (Details)	9 Months Ended
	Sep. 30, 2013 partnership property	Sep. 30, 2012 partnership property
Real Estate Properties [Line Items]
Number of apartment communities owned	2
Local Partnerships [Member]
Real Estate Properties [Line Items]
Number of Local Partnerships with limited equity interests	3	4
Number of apartment communities owned	2	4
Tradewinds Terrace [Member] | Traverse City, Michigan [Member]
Real Estate Properties [Line Items]
Number of units in apartment communities	122
Westport Village [Member] | Freeport, Illinois [Member]
Real Estate Properties [Line Items]
Number of units in apartment communities	121