EQUITY (Details) (USD $)	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended		3 Months Ended		0 Months Ended		3 Months Ended	0 Months Ended
	Mar. 31, 2013	Mar. 31, 2014 Series A Cumulative Redeemable Preferred Stock	Dec. 31, 2013 Series A Cumulative Redeemable Preferred Stock	Mar. 31, 2014 Series B Cumulative Redeemable Preferred Stock	Dec. 31, 2013 Series B Cumulative Redeemable Preferred Stock	Mar. 20, 2013 Series C Cumulative Redeemable Preferred Stock	Mar. 31, 2014 Series C Cumulative Redeemable Preferred Stock	Dec. 31, 2013 Series C Cumulative Redeemable Preferred Stock	Jan. 02, 2014 Common Stock	Jan. 03, 2013 Common Stock	Mar. 31, 2014 Common Stock	Mar. 31, 2013 Common Stock	Mar. 02, 2013 Common Stock Executive officers	Mar. 22, 2013 Common Stock Director	Mar. 31, 2014 Common Stock Director	Jan. 14, 2013 Common Stock Public offering	Feb. 14, 2011 Common Stock Private placement
Equity
New issued stock (in shares)						3,400,000										17,250,000	1,274,000
Proceeds from equity offerings, net of offering costs	$ 237,603,000					$ 81,700,000										$ 148,100,000
Underwriting discount and offering-related expenses						$ 3,300,000										$ 7,200,000
Shares of common stock issued to redeem common units									126,155	1,974,669	126,155	1,974,669
Stock issued to officers and directors (in shares)												293,704	292,090
Shares issued in lieu of cash for director fees														1,614	0
Preferred stock, dividend rate (as a percent)		9.25%	9.25%	7.875%	7.875%	7.125%	7.125%	7.125%
Preferred stock, liquidation preference (in dollars per share)		$ 25		$ 25			$ 25
Annual dividend rate per share (in dollars per share)		$ 2.3125		$ 1.96875			$ 1.78125