Consolidated Statements of Changes in Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Preferred Stock [Member] Series C Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
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	52,531						52,531
Other comprehensive income, net of income taxes	29,079					29,079
Cash dividends declared on common stock	(15,069)						(15,069)
Cash dividends paid on Series C Preferred Stock	(2,559)						(2,559)
Repurchases of common stock	(110,985)				(110,985)
Restricted share unit activity	(2,818)		175	(2,993)
Stock options exercised	456		27	429
Share-based compensation net tax deficiency	(900)			(900)
Share-based compensation expense	3,337			3,337
Balance at Mar. 31, 2016	2,953,268	125,980	140,794	2,989,854	(512,496)	(740)	209,876
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	71,857						71,857
Other comprehensive income, net of income taxes	908					908
Cash dividends declared on common stock	(18,347)						(18,347)
Cash dividends paid on Series C Preferred Stock	(2,559)						(2,559)
Repurchases of common stock	(15,151)				(15,151)
Restricted share unit activity	(7,784)		305	(7,799)			(290)
Stock options exercised	1,919		110	1,809
Share-based compensation expense	3,360			3,360
Balance at Mar. 31, 2017	$ 2,962,127	$ 125,980	$ 142,441	$ 3,025,775	$ (679,746)	$ (54,751)	$ 402,428