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	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator for basic net income per common share [Abstract]
Net income	$ 16,752	$ 16,440	$ 57,002	$ 65,423
Preferred stock dividends	(4,718)	(3,846)	(12,600)	(11,515)
Earnings participation of unvested equity awards	(36)	(40)	(116)	(123)
Numerator for basic net income per common share	$ 11,998	$ 12,554	$ 44,286	$ 53,785
Denominator for basic net income per common share [Abstract]
Average number of shares of common stock outstanding (in shares)	96,094	95,978	96,073	95,946
Average unvested stock awards outstanding (in shares)	(302)	(300)	(305)	(299)
Denominator for basic net income per common share (in shares)	95,792	95,678	95,768	95,647
Basic net income per common share (in dollars per share)	$ 0.13	$ 0.13	$ 0.46	$ 0.56
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	$ 11,998	$ 12,554	$ 44,286	$ 53,785
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share (in shares)	95,792	95,678	95,768	95,647
Net effect of dilutive equity awards (in shares)	131	188	137	152
Denominator for diluted net income per common share (in shares)	95,923	95,866	95,905	95,799
Diluted net income per common share (in dollars per share)	$ 0.13	$ 0.13	$ 0.46	$ 0.56