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, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator for basic net income per common share [Abstract]
Net income	$ 82,873	$ 108,325	$ 140,820
Preferred stock dividends	(15,372)	(15,160)	(13,781)
Earnings participation of unvested equity awards	(140)	(123)	(95)
Numerator for basic net income per common share	$ 67,361	$ 93,042	$ 126,944
Denominator for basic net income per common share [Abstract]
Average number of shares of common stock outstanding (in shares)	95,957	95,817	95,789
Average unvested stock awards outstanding (in shares)	(301)	(308)	(398)
Denominator for basic net income per common share (in shares)	95,656	95,509	95,391
Basic net income per common share (in dollars per share)	$ 0.70	$ 0.97	$ 1.33
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	$ 67,361	$ 93,042	$ 126,944
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share (in shares)	95,656	95,509	95,391
Net effect of dilutive equity awards (in shares)	163	192	238
Denominator for diluted net income per common share (in shares)	95,819	95,701	95,629
Diluted net income per common share (in dollars per share)	$ 0.70	$ 0.97	$ 1.33