NET INCOME PER COMMON SHARE - Components of Computation of Basic and Diluted Net Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator for basic net income per common share [Abstract]
Net income	$ 140,820	$ 126,487	$ 163,626
Redemption preference premiums paid on Convertible preferred stock	0	(19,924)	0
Preferred stock dividends	(13,781)	(17,536)	(21,021)
Earnings participation of unvested equity awards	(95)	(139)	(372)
Numerator for basic net income per common share	126,944	88,888	142,233
Denominator for basic net income per common share [Abstract]
Weighted average common stock outstanding (in shares)	95,789	95,679	95,115
Average unvested stock awards outstanding (in shares)	(398)	(506)	(522)
Denominator for basic net income per common share (in shares)	95,391	95,173	94,593
Basic net income per common share (in dollars per share)	$ 1.33	$ 0.93	$ 1.50
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	126,944	88,888	142,233
Dividends on dilutive convertible preferred stock	0	44	298
Numerator for diluted net income per common share	$ 126,944	$ 88,932	$ 142,531
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share	95,391	95,173	94,593
Net effect of dilutive equity awards (in shares)	238	145	111
Net effect of dilutive convertible preferred stock (in shares)	0	75	308
Denominator for diluted net income per common share (in shares)	95,629	95,393	95,012
Diluted net income per common share (in dollars per share)	$ 1.33	$ 0.93	$ 1.50