NET INCOME PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Numerator for basic net income per common share [Abstract]
Net income	$ 21,630	$ 24,944	$ 48,983	$ 58,901
Preferred stock dividends	(3,843)	(3,788)	(7,669)	(7,530)
Earnings participation of unvested equity awards	(39)	(33)	(83)	(67)
Numerator for basic net income per common share	$ 17,748	$ 21,123	$ 41,231	$ 51,304
Denominator for basic net income per common share [Abstract]
Average number of shares of common stock outstanding (in shares)	95,947	95,805	95,930	95,815
Average unvested stock awards outstanding (in shares)	(299)	(304)	(299)	(330)
Denominator for basic net income per common share (in shares)	95,648	95,501	95,631	95,485
Basic net income per common share (in dollars per share)	$ 0.19	$ 0.22	$ 0.43	$ 0.54
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	$ 17,748	$ 21,123	$ 41,231	$ 51,304
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share (in shares)	95,648	95,501	95,631	95,485
Net effect of dilutive equity awards (in shares)	138	188	135	197
Denominator for diluted net income per common share (in shares)	95,786	95,689	95,766	95,682
Diluted net income per common share (in dollars per share)	$ 0.19	$ 0.22	$ 0.43	$ 0.54
Redeemable Preferred Stock [Member] | Cumulative Redeemable Preferred Stock, Series E [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Preferred stock, dividend rate	7.50%		7.50%		7.50%