Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Series A Preferred Stock [Member]	Series E Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series A Preferred Stock [Member]	Retained Earnings [Member] Series E Preferred Stock [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss, Net of Tax [Member]
Beginning Balance at Dec. 31, 2013	$ 2,209,188			$ 151,649	$ 934	$ 1,125,584	$ 1,080,488			$ (100,918)	$ (48,549)
Cumulative effect of change in accounting principle at Dec. 31, 2013	160						160
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	98,263						98,263
Other comprehensive loss, net of tax	18,554										18,554
Dividends on common stock and dividend equivalents declared $0.43 and $0.35 per share during 6 months ended June 30, 2015 and 2014, respectively	(31,562)					23	(31,585)
Dividends on Series A preferred stock $21.25 and $42.50 per share and Series E preferred stock $800.00 per share for the 6 months ended June 30, 2015 and 2014, respectively	(5,278)	$ (1,230)	$ (4,048)					$ (1,230)	$ (4,048)
Common stock issued	436					436	0			0
Stock-based compensation, net of tax impact	6,246					3,431	1,285			1,530
Exercise of stock options	1,552					(1,174)				2,726
Shares acquired related to employee share-based compensation plans	(2,196)									(2,196)
Common stock repurchased	(10,741)									(10,741)
Ending Balance at Jun. 30, 2014	2,284,622			151,649	934	1,128,300	1,143,333			(109,599)	(29,995)
Beginning Balance at Dec. 31, 2014	2,322,815			151,649	936	1,127,534	1,202,251			(103,294)	(56,261)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102,225						102,225
Other comprehensive loss, net of tax	(4,434)										(4,434)
Dividends on common stock and dividend equivalents declared $0.43 and $0.35 per share during 6 months ended June 30, 2015 and 2014, respectively	(38,995)					56	(39,051)
Dividends on Series A preferred stock $21.25 and $42.50 per share and Series E preferred stock $800.00 per share for the 6 months ended June 30, 2015 and 2014, respectively	(4,663)	$ (615)	$ (4,048)					$ (615)	$ (4,048)
Common stock issued	0					0	0			0
Preferred Stock Conversions, Inducements	0			(28,939)		(3,429)				32,368
Stock-based compensation, net of tax impact	6,969					2,384	(672)			5,257
Exercise of stock options	2,477					(2,047)				4,524
Shares acquired related to employee share-based compensation plans	(4,074)									(4,074)
Common stock repurchased	(2,625)									(2,625)
Ending Balance at Jun. 30, 2015	$ 2,379,695			$ 122,710	$ 936	$ 1,124,498	$ 1,260,090			$ (67,844)	$ (60,695)