Description of Business (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended		4 Months Ended	11 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 01, 2003	Sep. 30, 2013	Mar. 31, 2013	Mar. 31, 2013	Dec. 31, 2014
Description of Business
Number of shares of common stock authorized for issuance	500,000,000	500,000,000						500,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01						$ 0.01
Number of shares of preferred stock authorized for issuance	100,000,000	100,000,000						100,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01						$ 0.01
Proceeds from issuance of common stock	$ 6,800,000	$ 134,176,328	$ 39,200,000
ACM
Description of Business
Structured finance assets contribution amount for commensurate equity ownership under operating partnership				213,100,000
Borrowings supported by equity contributed for commensurate equity ownership under operating partnership				169,200,000
Equity investment for commensurate equity ownership under operating partnership				43,900,000
Common Stock
Description of Business
Issuance of common stock (in shares)	1,000,000	17,625,000	7,000,000		6,000,000	5,625,000	6,000,000	1,000,000
Proceeds from issuance of common stock					$ 40,900,000	$ 43,000,000	$ 45,600,000	$ 6,500,000