EXCHANGEABLE SENIOR NOTES (Details) (USD $)	3 Months Ended		3 Months Ended	0 Months Ended			0 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 2033 Notes and 2027 Notes	Jun. 21, 2013 2.375% Exchangeable Senior Notes Operating Partnership	Mar. 31, 2014 2.375% Exchangeable Senior Notes Operating Partnership	Dec. 31, 2013 2.375% Exchangeable Senior Notes Operating Partnership	Jun. 21, 2013 2.375% Exchangeable Senior Notes Minimum Operating Partnership	Jun. 21, 2013 2.375% Exchangeable Senior Notes Maximum Operating Partnership
Notes payable
Principal amount of notes issued				$ 250,000,000	$ 250,000,000
Interest rate (as a percent)				2.375%	2.375%
Discount rate (as a percent)				1.50%
Issuance cost				1,672,000
Amortization period				5 years
Conversion ratio, number of shares per $1,000 principal amount, numerator				17.96
Principal amount used for debt instrument conversion ratio				1,000
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest				100.00%
Number of days of written notice to holders of notes required for redemption							30 days	60 days
Redemption price as percentage of principal amount of notes at request of debt holders and upon occurrence of designated event				100.00%
Carrying amount of the equity component, the principal amount of the liability component, its unamortized discount and its net carrying amount
Carrying amount of equity component					(14,496,000)	(14,496,000)
Principal amount of liability component	250,000,000	250,000,000			250,000,000	250,000,000
Unamortized discount - equity component					(12,469,000)	(13,131,000)
Unamortized cash discount	(15,637,000)	(16,487,000)		(3,750,000)	(3,168,000)	(3,356,000)
Net carrying amount of liability component					234,363,000	233,513,000
Effective interest rate on the liability component (as a percent)					4.00%
Amount of interest cost recognized relating to the contractual interest rate and the amortization of the discount on the liability component
Contractual interest			1,484,000
Amortization of discount	662,000		662,000
Total interest expense recognized			$ 2,146,000