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, 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)	0	(15)	(37,016)	0	0	0
Purchase of treasury stock	(8,613)	0	0	0	0	0	(8,613)
Cash dividends:
Common stock ($0.36 per share in 2017 and $0.45 per share in 2018)	(55,058)	0	0	0	(55,058)	0	0
Preferred stock	(7,008)	0	0	0	(7,008)	0	0
Issuance of preferred stock	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)
Beginning balance at Dec. 31, 2017	3,237,443	159,929	1,618	1,454,188	1,819,230	(62,758)	(134,764)
Comprehensive income:
Net income	244,578	0	0	0	244,578	0	0
Other comprehensive income	72,762	0	0	0	0		0
AOCI Loss Net of ASU Adoption and Tax	(59,024)					(59,024)
Adoption of new accounting standards	(13,738)	0	0	0	0	(13,738)	0
Comprehensive income	171,816
Common stock issued:
Stock-based compensation plans, net	17,393	0	0	3,134	(15,737)	0	29,996
Acquisitions	488,408	0	137	396,975	0	0	91,296
Purchase of common stock returned to authorized but unissued	(33,075)	0	(14)	(33,061)	0	0	0
Purchase of treasury stock	(124,380)	0	0	0	0	0	(124,380)
Cash dividends:
Common stock ($0.36 per share in 2017 and $0.45 per share in 2018)	(77,431)	0	0	0	(77,431)	0	0
Preferred stock	(7,077)	0	0	0	(7,077)	0	0
Issuance of preferred stock	97,315	97,315	0	0	0	0	0
Redemption of preferred stock	(646)	(528)	0	0	(118)	0	0
Common stock warrants exercised	0	0	11	(11)	0	0	0
Stock-based compensation expense, net	12,792	0	0	12,792	0	0	0
Tax Act Reclassification	13,654	0	0	0	13,654	0	0
Change in accounting principle	84	0	0	0	84	0	0
Other	742	0	0	0	742	0	0
Ending balance at Sep. 30, 2018	$ 3,797,038	$ 256,716	$ 1,752	$ 1,834,017	$ 1,977,925	$ (135,520)	$ (137,852)