Consolidated Statements of Changes in Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Preferred Stock Series C Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance at Dec. 31, 2015	$ 3,000,196	$ 125,980	$ 140,592	$ 2,989,981	$ (401,511)	$ (29,819)	$ 174,973
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	112,989						112,989
Other comprehensive income, net of income taxes	40,824					40,824
Cash dividends declared on common stock	(30,015)						(30,015)
Cash dividends paid on Series C Preferred Stock	(5,119)						(5,119)
Repurchases of common stock	(171,547)				(171,547)
Restricted share unit activity	(4,605)		298	(4,814)			(89)
Stock options exercised	2,035		118	1,917
Share-based compensation net tax benefit	52			52
Share-based compensation expense	6,849			6,849
Balance at Jun. 30, 2016	2,951,659	125,980	141,008	2,993,985	(573,058)	11,005	252,739
Balance at Dec. 31, 2016	2,927,924	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, 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	$ 125,980	$ 142,499	$ 3,029,754	$ (709,944)	$ (47,865)	$ 457,523