Equity (Details) (USD $)	1 Months Ended		3 Months Ended	12 Months Ended					1 Months Ended		12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended	0 Months Ended	1 Months Ended					12 Months Ended				0 Months Ended	1 Months Ended	12 Months Ended		0 Months Ended
	Jun. 30, 2007	Apr. 30, 2004	Mar. 31, 2011	Dec. 31, 2012	Feb. 01, 2013	Dec. 31, 2011	Jun. 30, 2010	May 31, 2009	Apr. 30, 2012 Non-management members of the Board of Directors	Jul. 31, 2011 Non-management members of the Board of Directors	Dec. 31, 2011 Non-management members of the Board of Directors Selling and administrative expense	Apr. 30, 2012 Director who was also the corporate secretary	Dec. 31, 2012 Director who was also the corporate secretary Selling and administrative expense	Mar. 31, 2012 Director is also an officer of the managing member of related party ACM	Dec. 31, 2012 Director is also an officer of the managing member of related party ACM Selling and administrative expense	Jan. 31, 2012 Director who was re-appointed to the board of directors on December 19, 2011	Dec. 31, 2011 Director who was re-appointed to the board of directors on December 19, 2011 Selling and administrative expense	Feb. 28, 2013 Employees of the company and a related party ACM Restricted common stock	Apr. 30, 2010 Independent members	Dec. 31, 2010 Independent members Selling and administrative expense	Jul. 03, 2012 Common Stock	Oct. 31, 2012 Common Stock	Jun. 30, 2012 Common Stock	Dec. 31, 2011 Common Stock	Mar. 31, 2011 Common Stock	Jun. 30, 2003 Common Stock	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Jun. 30, 2011 Common Stock	Dec. 31, 2012 Common Stock ATM equity offering sales agreement	Feb. 15, 2013 Common Stock ATM equity offering sales agreement Subsequent event	Dec. 31, 2011 Common Stock Employees of the company and a related party ACM	Dec. 31, 2011 Common Stock Employees of the company and a related party ACM Employee compensation and benefits	Dec. 31, 2011 Common Stock Employees of the company and a related party ACM Selling and administrative expense	Feb. 05, 2013 Preferred Stock 9.0% Series A Cumulative Redeemable Preferred Stock Subsequent event	Feb. 01, 2013 Preferred Stock 9.0% Series A Cumulative Redeemable Preferred Stock Subsequent event
Deferred Compensation
Number of fully vested shares issued									90,000	105,000		6,255		10,000		15,000			90,000													250,000
Accrued deferred compensation expense											$ 500,000		$ 500,000		$ 100,000		$ 100,000			$ 300,000													$ 400,000	$ 500,000
Granted (in shares)																		200,000
Additional stock reserved for issuance (in shares)								1,250,000
Vesting period																		2 years
Vesting percentage																		33.00%
Issuance of common stock (in shares)	2,700,000	6,750,000	666,927																			3,500,000	3,500,000		666,927	67	7,000,000	666,927			787,700					1,400,000
Common stock
Proceeds from issuance of shares under public offering	73,600,000	124,400,000		39,200,000																		19,200,000	17,500,000			1,005					5,500,000					33,600,000
Number of shares repurchased																					170,170			1,500,000
Total cost of shares repurchased																					700,000			5,700,000
Average cost (in dollars per share)																					$ 4.02			$ 3.83
Share price of shares of common stock sold under public offering																						$ 5.80	$ 5.40
Number of shares of common stock authorized to be repurchased under the stock repurchase program																								500,000				500,000	1,500,000
Number of shares which the entity may issue and sell through JMP																														6,000,000
Return on the preferred shares issued to third parties by its subsidiary REIT (as a percent)				12.50%																																9.00%
Additional shares for which an over-allotment option was granted to the underwriter																																				210,000
Option exercised by underwriters (in shares)																																			151,500
Additional net proceeds from exercise of option by underwriters																																			3,700,000
Number of shares of common stock authorized for issuance				500,000,000		500,000,000
Common stock, par value (in dollars per share)				$ 0.01		$ 0.01
Number of shares of preferred stock authorized for issuance				100,000,000		100,000,000
Preferred stock, par value (in dollars per share)				$ 0.01		$ 0.01
Aggregate amount of securities for which the entity filed shelf registration statement							500,000,000
Number of shares of common stock sold under public offering	2,700,000	6,750,000	666,927																			3,500,000	3,500,000		666,927	67	7,000,000	666,927			787,700					1,400,000
Number of shares of common stock remain available under shelf registration					$ 416,400,000
Common stock outstanding (in shares)				31,249,225		24,298,140