STOCKHOLDERS' EQUITY AND EARNINGS PER SHARE (Details) (USD $)	12 Months Ended			0 Months Ended		1 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 17, 2014	May 01, 2013	Apr. 30, 2008	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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Jan. 16, 2014	Jul. 17, 2013	Jan. 23, 2013	Jan. 19, 2012
Class of Stock
Common stock issued on conversion of convertible preferred stock		5,594,080
Final consideration (in shares)	5,583,093
Purchase of treasury stock pursuant to the Stock Repurchase Program, shares		8,026,807	9,068,105
Weighted average price of shares repurchased (in dollars per share)		$ 24.89	$ 22.02
Total cost of repurchase of treasury shares		$ 199,992,000	$ 199,950,000
Quarterly Dividends
Dividend per share (in dollars per share)	$ 0.72	$ 0.60	$ 0.40
MetroCorp
Class of Stock
Final consideration (in shares)				5,583,093
Final consideration in cash				89,400,000
Fair value of warrants				8,800,000
Cash paid to option holders				2,400,000
Warrants converted into the right to acquire shares																			771,429
Common stock equivalent to assumed obligation of holder's rights unexercised warrant (in shares)				230,282
Number of warrants exercised	0						0
Series A Non-Cumulative Perpetual Convertible Preferred Stock
Class of Stock
Number of shares issued during the period						200,000
Preferred stock dividend rate (as a percent)						8.00%
Preferred stock liquidation preference (in dollars per share)						$ 1,000
Proceeds from issuance of convertible preferred stock						194,100,000
Preferred shares converted					85,710
Common stock issued on conversion of convertible preferred stock					5,594,080
Quarterly Dividends
Dividend per share (in dollars per share)		$ 20.00	$ 20.00
Preferred stock cash dividends paid		3,400,000	6,900,000
Common Stock
Class of Stock
Amount of stock repurchase approved by the Board of Directors																				100,000,000	200,000,000	200,000,000
Quarterly Dividends
Dividend per share (in dollars per share)							$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.10	$ 0.10	$ 0.10	$ 0.10
Common stock cash dividends paid	$ 104,000,000	$ 83,300,000	$ 57,600,000
Common Stock | MetroCorp
Class of Stock
Final consideration (in shares)				5,583,093