Subsequent events Refinancing of Mortagage loans (Details) (USD $)	Breakwater Bay apartments USD ($)	Northside on Travis apartments	Capitol Hill apartments	Mansfield apartments	Pecan Creek apartments
Balance of Mortagage loans at Dec. 31, 2012	$ 0
Number of units.	176	200	156	208	192
New mortgage in millions.	9.8	13.9	9.4	16.3	15.1
Paid off the existing mortgage in millions.	9.1	13.5	8.8	15.8	14.6
Closing costs and escrow reserves paid in millions.	0.7	1.3	0.6	1.4	1.2
Notes accrued interest rate.	2.50%	2.50%	2.50%	2.50%	2.50%
Amortization schedule in years.	40	40	40	40	40
Balance of Mortagage loans. at Feb. 28, 2013	$ 0