Related-Party Transactions (Details) (Manager, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Factor D Y quarter M fee	Sep. 30, 2010	Dec. 31, 2010
Manager
Related-Party Transactions
Initial term of management agreement (in years)			3
Term of each agreement extension (in years)			1
Base management fee as a percentage of stock holders' equity (as a percent)			1.50%
Base management fee incurred	$ 6.7	$ 3.4	$ 17.6	$ 10.3
Base management fee payable	6.7	3.5	6.7	3.5
Threshold percentage of Core Earnings for payment of incentive fee (as a percent)			8.00%
Period for calculation of threshold Core Earnings percentage (in months)			12
Number of prior calendar quarters for calculation of threshold Core Earnings amount (in months)			12
Minimum incentive fees			0
Incentive fee calculation, multiplication factor (as a percent)			20.00%
Incentive fee calculation, period (in months)			12
Incentive fee calculation, stock value factor (as a percent)			8.00%
Number of calendar quarters of incentive fee paid subtracted in incentive fee calculation (in months)			3
Portion of incentive fee quarterly installment payable in shares			0.50
Stock ownership limit (as a percent)			9.80%
Number of trading days price used to calculate average stock price for payment of incentive fees in shares (in days)			5
Increase in incentive fee accrual	0.4		1.2
Incentive fee payable					1.2
Executive compensation and other reimbursable expenses	1.0	0.4	2.8	1.2
Executive compensation and other reimbursable expense payable	$ 1.1	$ 0.2	$ 1.1	$ 0.2
Affirmative vote required by Company's independent directors for termination of management agreement without cause			two-thirds
Notice period for termination of management agreement without cause (in days)			180
Termination fee, factor applied to average base and incentive management fees			3
Termination period of calculation (calendar quarters)			8
Notice period for termination of management agreement with cause (in days)			30