STOCKHOLDERS' EQUITY (Details) - USD ($)		1 Months Ended	12 Months Ended
	Feb. 26, 2016	May. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 27, 2016
Class of Stock [Line Items]
Redemption preference premiums paid			$ 0	$ 0	$ 19,924,000
Subsequent Event [Member]
Class of Stock [Line Items]
Common stock repurchase program						$ 100,000,000
Shares repurchased (in shares)	0
Cumulative Redeemable Preferred Stock, Series E [Member]
Class of Stock [Line Items]
Redeemable preferred stock, shares issued (in shares)		6,800,000
Redeemable preferred stock, face value		$ 170,000,000
Preferred stock dividend rate		7.50%
Redeemable preferred stock, liquidation preference per share (in dollars per share)		$ 25.00
Cash on hand used in capital transactions		$ 42,700,000
Net proceeds		$ 164,300,000
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Cash used for redemption of preferred stock					207,000,000
Redemption preference premiums paid					$ 19,900,000
Reduction in income per share (in dollars per share)					$ 0.21
Continuous Offering Program [Member] | Cumulative Redeemable Preferred Stock, Series E [Member]
Class of Stock [Line Items]
Shares (in shares)			538,000	757,000	61,000
Net issue price (in dollars per share)			$ 24.61	$ 24.01	$ 23.78
Net proceeds			$ 13,236,000	$ 18,180,000	$ 1,447,000
Directors And Employees [Member]
Class of Stock [Line Items]
Additions to common equity capital related to equity-based awards			$ 1,700,000	$ 1,900,000	$ 1,800,000