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, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator for basic net income per common share [Abstract]
Net income	$ 50,072	$ 79,589	$ 82,873
Preferred stock dividends	(19,368)	(17,442)	(15,372)
Earnings participation of unvested stock awards	(102)	(150)	(140)
Numerator for basic net income per common share	$ 30,602	$ 61,997	$ 67,361
Denominator for basic net income per common share [Abstract]
Average number of shares of common stock outstanding (in shares)	91,565	96,023	95,957
Average unvested stock awards outstanding (in shares)	(451)	(305)	(301)
Denominator for basic net income per common share (in shares)	91,114	95,718	95,656
Basic net income per common share (in dollars per share)	$ 0.34	$ 0.65	$ 0.70
Numerator for diluted net income per common share [Abstract]
Numerator for basic net income per common share	$ 30,602	$ 61,997	$ 67,361
Denominator for diluted net income per common share [Abstract]
Denominator for basic net income per common share (in shares)	91,114	95,718	95,656
Net effect of dilutive equity-based awards (in shares)	116	125	163
Denominator for diluted net income per common share (in shares)	91,230	95,843	95,819
Diluted net income per common share (in dollars per share)	$ 0.34	$ 0.65	$ 0.70