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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU	$ 0
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)			0	(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
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	125,980	142,678	3,043,129	(839,674)	(54,754)	544,207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	103,166						103,166
Other comprehensive income, net of income taxes	(45,552)					(45,552)
Cash dividends declared on common stock	(29,675)						(29,675)
Cash dividends paid on Series C Preferred Stock	(2,559)						(2,559)
Repurchases of common stock	(26,733)				(26,733)
Restricted share unit activity	(8,228)		266	(8,494)
Stock options exercised	1,240		73	1,167
Share-based compensation expense	3,955			3,955
Balance at Mar. 31, 2018	2,956,495	$ 125,980	$ 143,017	$ 3,039,757	$ (866,407)	$ (107,777)	$ 621,925
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU | ASU 2016-01	$ 3,200