STOCKHOLDERS' EQUITY AND EARNINGS PER SHARE (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
STOCKHOLDERS' EQUITY AND EARNINGS PER SHARE
Common stock, shares outstanding	143,582,229				137,630,896				143,582,229	137,630,896
Earnings per share calculations
Net income	$ 92,998	$ 88,756	$ 83,988	$ 76,741	$ 75,782	$ 73,157	$ 74,015	$ 72,091	$ 342,483	$ 295,045	$ 281,650
Less: Preferred stock dividends							(1,714)	(1,714)		(3,428)	(6,857)
Less: Earnings allocated to participating securities									(502)	(1,692)	(3,279)
Basic EPS - income allocated to common stockholders									341,981	289,925	271,514
Effect of dilutive securities:
Restricted stock units									287	196	47
Convertible preferred stock										3,428	6,857
Diluted EPS - income allocated to common stockholders									$ 342,268	$ 293,549	$ 278,418
Number of Shares
Weighted average shares outstanding									142,952,000	137,342,000	141,457,000
Effect of dilutive securities on weighted average shares outstanding
Stock options (in shares)									67,000	71,000	29,000
Restricted stock units (in shares)									398,000	327,000	118,000
Convertible preferred stock (in shares)										1,834,000	5,571,000
Warrants (in shares)									146,000
Total weighted average diluted shares outstanding									143,563,000	139,574,000	147,175,000
Per Share Amounts
Basic EPS - income allocated to common stockholders (in dollars per share)	$ 0.65	$ 0.62	$ 0.59	$ 0.54	$ 0.55	$ 0.53	$ 0.52	$ 0.51	$ 2.39	$ 2.11	$ 1.92
Diluted EPS - Income available to common stockholders (in dollars per share)	$ 0.65	$ 0.62	$ 0.58	$ 0.54	$ 0.55	$ 0.53	$ 0.52	$ 0.50	$ 2.38	$ 2.10	$ 1.89