ISSUANCES OF COMMON STOCK (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended				12 Months Ended
	Aug. 13, 2012	Dec. 06, 2011	Nov. 10, 2010	Apr. 19, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
ISSUANCES OF COMMON STOCK
Issuance of stock on underwritten public offering (in shares)	6.3	3.6	11.5	4.2
Price of common stock (in dollars per share)	$ 9.75	$ 8.00	$ 6.00	$ 4.50	$ 10.59
Net proceeds received from the offerings	$ 57,800,000	$ 27,200,000	$ 64,700,000	$ 17,600,000	$ 57,755,000	$ 27,215,000	$ 82,327,000
Underwriting discount and other stock issuance costs	$ 3,900,000	$ 1,500,000	$ 4,300,000	$ 1,300,000