STOCKHOLDERS' EQUITY (Details) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 30, 2010
Stockholders' Equity
Maximum value of securities for which the entity filed a shelf registration statement			$ 200,000,000		$ 150,000,000
Common stock issued (in shares)	7,813,483	21,613,483	12,075,000	11,500,000
Net proceeds from sale of common stock		295,697,000	83,784,000	36,023,000
Net proceeds from sale of stock in an underwritten public offering		278,563,000	43,483,000	33,695,000
Preferred stock, shares authorized	3,000,000	3,000,000	3,000,000
Class C Preferred Stock
Stockholders' Equity
Preferred stock, shares authorized	3,000,000	3,000,000
Series C-1 Preferred Stock
Stockholders' Equity
Preferred stock, shares authorized	350,000	350,000
Cantor Amendment
Stockholders' Equity
Common stock issued (in shares)		2,433,608	8,003,290	575,000
Net proceeds from sale of common stock		$ 17,100,000	$ 40,100,000	$ 2,200,000
Shareholder Rights Plan
Shareholder Rights Plan
Number of multiples of the exercise price that the Right holder has a right to receive in value of the acquiring company's common stock		2
Shareholder Rights Plan | Minimum
Shareholder Rights Plan
Percentage of assets or earning power sold allowing the Right holder a right to receive common stock of the acquiring company		50.00%
Shareholder Rights Plan | Series C-1 Preferred Stock
Shareholder Rights Plan
Number of preferred stock purchase rights for each outstanding share of common stock		1
Number of shares callable by rights	0.0001	0.0001
Exercise price (in dollars per unit)	35.00	35.00
Number of multiples of the exercise price that the Right holder has right to receive in value if 15% or more of the outstanding common stock is acquired		2
Shareholder Rights Plan | Series C-1 Preferred Stock | Minimum
Shareholder Rights Plan
Percentage of common stock to be acquired for rights to be exercisable		15.00%
Percentage of common stock to be acquired in a tender offer for rights to be exercisable		15.00%