Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Significant Accounting Policies
Ownership interest in subsidiaries (as a percent)	100.00%
External commissions	$ 27,900,000	$ 18,200,000	$ 18,700,000
Percentage of external commissions to housing revenues	2.20%	2.10%	1.90%
Cash and cash equivalents	155,692,000	159,113,000
Restricted cash deposits kept as collateral for outstanding letters of credit	70,300,000	56,700,000
Restricted cash
Restricted cash	70,893,000	57,049,000
RMC
Restricted cash
Restricted cash	$ 627,000	$ 391,000