Subsequent Events (Details) (USD $)	1 Months Ended
	Jan. 31, 2012 Convertible notes due 2012	Apr. 30, 2012 Convertible note repayment Convertible notes due 2012	Apr. 30, 2012 Debt amendment Fannie Mae	Apr. 27, 2012 Debt amendment Fannie Mae
Subsequent Events
Debt Instrument, Decrease, Repayments	$ 51,000,000	$ 199,000,000
Maximum borrowing capacity				1,000,000,000
Minimum net worth threshold, base amount				1,000,000,000
Numerator for the ratio of indebtedness to tangible net worth, maximum			6.5
Denominator for the ratio of indebtedness to tangible net worth, maximum			1
Minimum amount to be maintained in facilities				1,000,000,000
Maximum amount to be maintained in gestation facilities				$ 500,000,000