Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Equity	Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2015	$ 2,937,246	$ 121,379	$ 1,642	$ 1,458,522	$ 1,593,239	$ (32,616)	$ (204,920)
Comprehensive income:
Net income	91,625	0	0	0	91,625	0	0
Other comprehensive income	46,069	0	0	0	0	46,069	0
Comprehensive income	137,694
Common stock issued:
Stock-based compensation plans, net	4,276	0	0	1,153	(17,478)	0	20,601
Purchase of common stock returned to authorized but unissued	(20,007)	0	(12)	(19,995)	0	0	0
Purchase of treasury stock	(4,018)	0	0	0	0	0	(4,018)
Cash dividends:
Common stock dividends ($0.22 per share in 2016 and $0.24 per share in 2017)	(33,034)	0	0	0	(33,034)	0	0
Preferred stock dividends	(4,367)	0	0	0	(4,367)	0	0
Purchase of preferred stock	(1,248)	(1,178)	0	0	(70)	0	0
Stock-based compensation expense, net	13,210	0	0	13,210	0	0	0
Tax impact of stock-based compensation	395	0	0	395	0	0	0
Ending balance at Jun. 30, 2016	3,030,147	120,201	1,630	1,453,285	1,629,915	13,453	(188,337)
Beginning balance at Dec. 31, 2016	3,091,312	159,929	1,630	1,459,498	1,695,764	(54,679)	(170,830)
Comprehensive income:
Net income	114,253	0	0	0	114,253	0	0
Other comprehensive income	1,209	0	0	0	0	1,209	0
Comprehensive income	115,462
Common stock issued:
Stock-based compensation plans, net	20,945	0	0	1,102	(20,912)	0	40,755
Purchase of treasury stock	(8,445)	0	0	0	0	0	(8,445)
Cash dividends:
Common stock dividends ($0.22 per share in 2016 and $0.24 per share in 2017)	(36,804)	0	0	0	(36,804)	0	0
Preferred stock dividends	(4,669)	0	0	0	(4,669)	0	0
Stock-based compensation expense, net	12,667	0	0	12,667	0	0	0
Other	1,034	0	0	1,034	0	0	0
Ending balance at Jun. 30, 2017	$ 3,191,502	$ 159,929	$ 1,630	$ 1,474,301	$ 1,747,632	$ (53,470)	$ (138,520)