Related-Party Transactions (Details) (Manager, USD $) In Millions, unless otherwise specified	4 Months Ended	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2011 M multiplier calendarquarter D Y	Dec. 31, 2010	Dec. 31, 2009
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		1.50%
Base management fee incurred		$ 24.2	$ 14.1	$ 5.1
Base management Fee Payable		6.7	3.8
Threshold percentage of Core Earnings for payment of incentive fee		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		12
Threshold amount of Core Earnings for payment of incentive fee		0
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		3
Portion of incentive fee quarterly installment payable in shares (as a percent)		50.00%
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
Incentive fee payable			1.2
Increase in incentive fee accrual		1.2
Executive compensation and other reimbursable expenses	0.2	4.0	1.6
Executive compensation and other reimbursable expense payable		$ 1.7	$ 0.3
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 (in quarters)		8
Notice period for termination of management agreement with cause (in days)		30