EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended		5 Months Ended	6 Months Ended
	Jan. 15, 2016	Aug. 20, 2015	Aug. 30, 2015	Jun. 30, 2017	Jun. 30, 2016	Jan. 15, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic earnings per common share
Net income				$ 95,686	$ 129,460		$ 115,542	$ 177,846
Less: preferred share dividends				10,656	9,969		25,497	19,938
Net income available to common shareholders				$ 85,030	$ 119,491		$ 90,045	$ 157,908
Weighted average number of common shares outstanding - basic (in shares)				84,141,000	91,926,000		85,076,000	92,980,000
Basic earnings per common share (in usd per share)				$ 1.01	$ 1.30		$ 1.06	$ 1.70
Diluted earnings per common share
Net income available to common shareholders				$ 85,030	$ 119,491		$ 90,045	$ 157,908
Weighted average number of common shares outstanding - basic (in shares)				84,141,000	91,926,000		85,076,000	92,980,000
Share based compensation plans (in shares)				370,000	632,000		571,000	725,000
Weighted average number of common shares outstanding - diluted (in shares)				84,511,000	92,558,000		85,647,000	93,705,000
Diluted earnings per common share (in usd per share)				$ 1.01	$ 1.29		$ 1.05	$ 1.69
Anti-dilutive shares excluded from the dilutive computation (in shares)				16,000	7,000		284,000	339,000
August 17, 2015 ASR agreement [Member]
Diluted earnings per common share
Shares repurchased (in shares)	1,358,380.00	4,149,378	4,149,378			5,507,758