Stockholders' Equity (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended			3 Months Ended	12 Months Ended	50 Months Ended
	Mar. 31, 2013	Feb. 28, 2013	Jan. 31, 2013	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013
Common Stock
Number of shares of common stock sold pursuant to primary offering				17.4	43.4	76.5
Gross proceeds from issuance of common stock				$ 173,500,000	$ 433,000,000	$ 761,800,000
Distribution Reinvestment Plan
Initial purchase price per share under the DRP (in dollars per share)				$ 9.50
Price of shares issued as a percentage of estimated value per share				95.00%
Period within which the company expects to establish an estimated value per share				18 months
Selling commissions or dealer manager fees that will be paid for sales under DRP				0
Notice period served by board of directors to amend or terminate DRP				10 days
Shares sold pursuant to DRP				0.6	1.1	1.8
Total proceeds from sale of shares pursuant to DRP				5,242,000	10,305,000	17,100,000
Distributions
Daily amount of distribution accrued per share (in dollars per share)				$ 0.002185792
Annual distribution rate (as a percent)				8.00%
Cash	2,909,000	2,378,000	2,441,000	13,464,000	27,922,000
DRP	2,163,000	1,778,000	1,795,000
Total	5,072,000	4,156,000	4,236,000
Share Repurchase Program
Holding period of shares required for repurchase				1 year
Number of shares repurchased				0.1	0.1
Total amount of shares repurchased				$ 1,019,000	$ 1,371,000
Repurchase price paid per share (in dollars per share)				$ 9.74	$ 9.62