Debt Financing Total Debt Financing (Details) (USD $)	12 Months Ended			3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013		Sep. 30, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Debt financing	$ 345,359,000	$ 257,274,000
Trading Securities [Member]
Debt Instrument [Line Items]
Debt financing	174,250,000	164,295,000
Trading Securities [Member] | TOB facility-2 [Member]
Debt Instrument [Line Items]
Debt financing	44,675,000	48,995,000
Date of Debt Borrowing	2012	2012
Available-for-sale Security, Maturity Date at a point in time	Jun. 01, 2015	Jun. 01, 2014
Debt Instrument, Total Rate of Borrowing	2.20%	2.32%
Trading Securities [Member] | TOB Facility-1 [Member]
Debt Instrument [Line Items]
Debt financing		9,770,000		9,800,000	9,800,000
Date of Debt Borrowing		2011
Available-for-sale Security, Maturity Date at a point in time		Jul. 01, 2014
Debt Instrument, Total Rate of Borrowing		1.96%
Trading Securities [Member] | TOB facility-5 [Member]
Debt Instrument [Line Items]
Debt financing		5,700,000
Date of Debt Borrowing		2013
Available-for-sale Security, Maturity Date at a point in time		Jun. 01, 2014
Debt Instrument, Total Rate of Borrowing		2.40%
Trading Securities [Member] | TOB facility-6 [Member]
Debt Instrument [Line Items]
Debt financing		7,000,000
Date of Debt Borrowing		2013
Available-for-sale Security, Maturity Date at a point in time		Aug. 01, 2014
Debt Instrument, Total Rate of Borrowing		2.40%
Trading Securities [Member] | TOB facility-7 [Member]
Debt Instrument [Line Items]
Debt financing		20,000,000	[1]
Date of Debt Borrowing		2013	[1]
Available-for-sale Security, Maturity Date at a point in time		Jun. 01, 2014	[1]
Debt Instrument, Total Rate of Borrowing		2.21%	[1]
Trading Securities [Member] | TOB facility-8 [Member]
Debt Instrument [Line Items]
Debt financing		13,210,000	[2]
Date of Debt Borrowing		2013	[2]
Available-for-sale Security, Maturity Date at a point in time		Oct. 01, 2014	[2]
Debt Instrument, Total Rate of Borrowing		2.21%	[2]
Trading Securities [Member] | TOB facility-9 [Member]
Debt Instrument [Line Items]
Debt financing	25,535,000	25,750,000
Date of Debt Borrowing	2013	2013
Available-for-sale Security, Maturity Date at a point in time	Jun. 01, 2015	Dec. 01, 2014
Debt Instrument, Total Rate of Borrowing	1.96%	1.96%
Trading Securities [Member] | TOB Facility-10 [Member]
Debt Instrument [Line Items]
Debt financing	21,850,000
Date of Debt Borrowing	2014
Available-for-sale Security, Maturity Date at a point in time	Oct. 01, 2016			Oct. 01, 2016
Debt Instrument, Total Rate of Borrowing	4.34%
Trading Securities [Member] | TOB Facility-11 [Member]
Debt Instrument [Line Items]
Debt financing	34,975,000
Date of Debt Borrowing	2014
Available-for-sale Security, Maturity Date at a point in time	Jul. 01, 2019			Jul. 01, 2019
Debt Instrument, Total Rate of Borrowing	4.47%
Trading Securities [Member] | TOB Facility-12 [Member] [Member]
Debt Instrument [Line Items]
Debt financing	17,250,000
Date of Debt Borrowing	2014
Available-for-sale Security, Maturity Date at a point in time	Jul. 01, 2017			Jul. 01, 2017
Debt Instrument, Total Rate of Borrowing	4.55%
Trading Securities [Member] | TOB facility-13 [Member]
Debt Instrument [Line Items]
Debt financing	9,010,000
Date of Debt Borrowing	2014
Available-for-sale Security, Maturity Date at a point in time	Jul. 01, 2017
Debt Instrument, Total Rate of Borrowing	4.05%
Trading Securities [Member] | TOB facility-14 [Member]
Debt Instrument [Line Items]
Debt financing	9,010,000
Date of Debt Borrowing	2014
Available-for-sale Security, Maturity Date at a point in time	Jul. 01, 2017
Debt Instrument, Total Rate of Borrowing	4.05%
Trading Securities [Member] | Mortgage Backed Security Trust 1 [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing	2,585,000	2,585,000
Date of Debt Borrowing	2012	2012
Available-for-sale Security, Maturity Date at a point in time	Apr. 01, 2015	Apr. 01, 2014
Debt Instrument, Total Rate of Borrowing	1.12%	1.21%
Trading Securities [Member] | Mortgage Backed Security Trust 2 [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing	4,090,000	4,090,000
Date of Debt Borrowing	2012	2012
Available-for-sale Security, Maturity Date at a point in time	Apr. 01, 2015	Apr. 01, 2014
Debt Instrument, Total Rate of Borrowing	1.12%	1.29%
Trading Securities [Member] | Mortgage Backed Security Trust 3 [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing		2,865,000			2,900,000
Date of Debt Borrowing		2012
Available-for-sale Security, Maturity Date at a point in time		Apr. 01, 2014
Debt Instrument, Total Rate of Borrowing		1.22%
Trading Securities [Member] | Mortgage Backed Security Trust 4 [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing		5,960,000
Date of Debt Borrowing		2012
Available-for-sale Security, Maturity Date at a point in time		Apr. 01, 2014
Debt Instrument, Total Rate of Borrowing		1.23%
Trading Securities [Member] | Mortgage Backed Security Trust 5 [Member] [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing	5,270,000	10,545,000
Date of Debt Borrowing	2012	2012
Available-for-sale Security, Maturity Date at a point in time	Apr. 01, 2015	Apr. 01, 2014
Debt Instrument, Total Rate of Borrowing	1.06%	1.27%
Trading Securities [Member] | Mortgage Backed Security Trust 6 [Member] | TOB facility-3 [Member]
Debt Instrument [Line Items]
Debt financing		$ 7,825,000
Date of Debt Borrowing		2013
Available-for-sale Security, Maturity Date at a point in time		Aug. 01, 2014
Debt Instrument, Total Rate of Borrowing		1.02%

[1] Avistar at Chase Hill, Avistar at the Crest, and Avistar on the Boulevard is the collateral for the approximate $13.2 million TOB Trust.

[2] Avistar at the Oaks Apartments, Avistar on the Hills Apartments, and Avistar in 09 Apartments is the collateral for the $20.0 million TOB Trust.