CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (unaudited) - USD ($) $ in Thousands	Total	Preferred Stock Series D Preferred Stock	Preferred Stock Series C Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU	$ 0
Balance at Dec. 31, 2016	2,927,924	$ 0	$ 125,980	$ 142,026	$ 3,028,405	$ (664,595)	$ (55,659)	$ 351,767
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	147,861							147,861
Other comprehensive income (loss), net of income taxes	7,794						7,794
Cash dividends declared on common stock	(36,696)							(36,696)
Cash dividends paid on Series C Preferred Stock	(5,119)							(5,119)
Repurchases of common stock	(45,349)					(45,349)
Restricted share unit activity	(7,810)			330	(7,850)			(290)
Stock options exercised	2,504			143	2,361
Share-based compensation expense	6,838				6,838
Balance at Jun. 30, 2017	2,997,947	0	125,980	142,499	3,029,754	(709,944)	(47,865)	457,523
Balance at Mar. 31, 2017							(54,751)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of income taxes	6,886						6,886
Balance at Jun. 30, 2017	2,997,947	0	125,980	142,499	3,029,754	(709,944)	(47,865)	457,523
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU	(685)
Adoption of ASU | ASU 2014-09	(685)							(685)
Adoption of ASU | ASU 2018-02	0						(7,588)	7,588
Adoption of ASU | ASU 2016-01	0						117	(117)
Balance at Dec. 31, 2017	2,961,566	0	125,980	142,678	3,043,129	(839,674)	(54,754)	544,207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	214,348							214,348
Other comprehensive income (loss), net of income taxes	(63,495)						(63,495)
Cash dividends declared on common stock	(59,185)							(59,185)
Cash dividends paid on Series C Preferred Stock	(5,119)							(5,119)
Issuance of Series D Preferred Stock, net of issuance costs	195,138	195,138
Repurchases of common stock	(76,810)					(76,810)
Restricted share unit activity	(8,280)			289	(8,220)			(349)
Stock options exercised	1,896			111	1,785
Share-based compensation expense	8,320				8,320
Balance at Jun. 30, 2018	3,167,694	195,138	125,980	143,078	3,045,014	(916,484)	(125,720)	700,688
Balance at Mar. 31, 2018							(107,777)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss), net of income taxes	(17,943)						(17,943)
Balance at Jun. 30, 2018	3,167,694	$ 195,138	$ 125,980	$ 143,078	$ 3,045,014	$ (916,484)	$ (125,720)	$ 700,688
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU | ASU 2016-01	$ 3,200