Investments in Partnerships - Apartment Communities Owned (Details)	6 Months Ended
	Jun. 30, 2013 partnership	Jun. 30, 2012 partnership
Local Partnerships [Member]
Real Estate Properties [Line Items]
Number of Local Partnerships with limited equity interests	3	4
Northridge Park [Member] | Salinas, California [Member]
Real Estate Properties [Line Items]
Number of units in apartment communities	104
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