NET INCOME PER COMMON SHARE - Components of Computation of Basic and Diluted Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Numerator for basic net income per common share [Abstract]
Net income	$ 108,325	$ 140,820	$ 126,487
Preferred stock dividends	(15,160)	(13,781)	(17,536)
Redemption preference premiums paid on Convertible preferred stock	0	0	(19,924)
Earnings participation of unvested equity awards	(123)	(95)	(139)
Numerator for basic net income per common share	$ 93,042	$ 126,944	$ 88,888
Denominator for basic net income per common share [Abstract]
Average number of shares of common stock outstanding (in shares)	95,817	95,789	95,679
Average unvested stock awards outstanding (in shares)	(308)	(398)	(506)
Denominator for basic net income per common share (in shares)	95,509	95,391	95,173
Basic net income per common share (in dollars per share)	$ 0.97	$ 1.33	$ 0.93
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	$ 93,042	$ 126,944	$ 88,888
Dividends on dilutive convertible preferred stock	0	0	44
Numerator for diluted net income per common share	$ 93,042	$ 126,944	$ 88,932
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share (in shares)	95,509	95,391	95,173
Net effect of dilutive equity awards (in shares)	192	238	145
Net effect of dilutive convertible preferred stock (in shares)	0	0	75
Denominator for diluted net income per common share (in shares)	95,701	95,629	95,393
Diluted net income per common share (in dollars per share)	$ 0.97	$ 1.33	$ 0.93