EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic earnings per common share
Net income	$ 103,514	$ 95,686	$ 176,719	$ 115,542
Less: preferred share dividends	10,656	10,656	21,313	25,497
Net income available to common shareholders	$ 92,858	$ 85,030	$ 155,406	$ 90,045
Weighted average number of common shares outstanding - basic (in shares)	83,539	84,141	83,431	85,076
Basic earnings per common share (in usd per share)	$ 1.11	$ 1.01	$ 1.86	$ 1.06
Diluted earnings per common share
Net income available to common shareholders	$ 92,858	$ 85,030	$ 155,406	$ 90,045
Weighted average number of common shares outstanding - basic (in shares)	83,539	84,141	83,431	85,076
Share based compensation plans (in shares)	445	370	422	571
Weighted average number of common shares outstanding - diluted (in shares)	83,984	84,511	83,853	85,647
Diluted earnings per common share (in usd per share)	$ 1.11	$ 1.01	$ 1.85	$ 1.05
Weighted average anti-dilutive shares excluded from the dilutive computation (in shares)	158	16	484	284