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	145,441	0	0	0	145,441	0	0
Other comprehensive income	31,362	0	0	0	0	31,362	0
Comprehensive income	176,803
Common stock issued:
Stock-based compensation plans, net	7,749	0	0	1,785	(18,070)	0	24,034
Purchase of common stock returned to authorized but unissued	(20,007)	0	(12)	(19,995)	0	0	0
Purchase of treasury stock	(4,243)	0	0	0	0	0	(4,243)
Cash dividends:
Common stock dividends ($0.33 per share in 2016 and $0.36 per share in 2017)	(49,642)	0	0	0	(49,642)	0	0
Preferred stock dividends	(6,555)	0	0	0	(6,555)	0	0
Issuance of preferred stock	97,066	97,066	0	0	0	0	0
Redemption of preferred stock	(58,903)	(57,338)	0	0	(1,565)	0	0
Purchase of preferred stock	(1,248)	(1,178)	0	0	(70)	0	0
Stock-based compensation expense, net	18,047	0	0	18,047	0	0	0
Other	802	0	0	802	0	0	0
Ending balance at Sep. 30, 2016	3,097,115	159,929	1,630	1,459,161	1,662,778	(1,254)	(185,129)
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	179,254	0	0	0	179,254	0	0
Other comprehensive income	391	0	0	0	0	391	0
Comprehensive income	179,645
Common stock issued:
Stock-based compensation plans, net	22,460	0	0	1,952	(20,768)	0	41,276
Purchase of common stock returned to authorized but unissued	(37,031)		(15)	(37,016)	0	0	0
Purchase of treasury stock	(8,613)	0	0	0	0	0	(8,613)
Cash dividends:
Common stock dividends ($0.33 per share in 2016 and $0.36 per share in 2017)	(55,058)	0	0	0	(55,058)	0	0
Preferred stock dividends	(7,008)	0	0	0	(7,008)	0	0
Stock-based compensation expense, net	16,860	0	0	16,860	0	0	0
Other	1,034	0	0	1,034	0	0	0
Ending balance at Sep. 30, 2017	$ 3,203,601	$ 159,929	$ 1,615	$ 1,442,328	$ 1,792,184	$ (54,288)	$ (138,167)