Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive income (loss)	Series C preferred stock	Series C preferred stock Preferred stock	Series C preferred stock Common stock	Series C preferred stock Surplus
Balance at beginning of period at Dec. 31, 2016	$ 2,695,617	$ 251,257	$ 51,978	$ 1,365,781	$ (4,589)	$ 1,096,518	$ (65,328)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	257,682					257,682
Other comprehensive income (loss), net of tax	23,493						23,493
Cash dividends declared on common stock	(30,765)					(30,765)
Dividends on preferred stock	(9,778)					(9,778)
Stock-based compensation	12,858			12,858
Conversion of Series C Preferred Stock to common stock								$ 0	$ (126,257)	$ 3,121	$ 123,136
Common stock issued for:
Acquisitions	0
Exercise of stock options and warrants	24,074		813	23,261
Restricted stock awards	(397)		88	(88)	(397)
Employee stock purchase plan	2,530		36	2,494
Director compensation plan	1,625		32	1,593
Balance at end of period at Dec. 31, 2017	2,976,939	125,000	56,068	1,529,035	(4,986)	1,313,657	(41,835)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment from adoption | ASU 2018-02	0					2,974	(2,974)
Net income	343,166					343,166
Other comprehensive income (loss), net of tax	(30,183)						(30,183)
Cash dividends declared on common stock	(42,787)					(42,787)
Dividends on preferred stock	(8,200)					(8,200)
Stock-based compensation	13,496			13,496
Common stock issued for:
Acquisitions	0
Exercise of stock options and warrants	11,466		299	11,359	(192)
Restricted stock awards	(456)		101	(101)	(456)
Employee stock purchase plan	2,523		31	2,492
Director compensation plan	1,722		19	1,703
Balance at end of period at Dec. 31, 2018	3,267,570	125,000	56,518	1,557,984	(5,634)	1,610,574	(76,872)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	355,697					355,697
Other comprehensive income (loss), net of tax	42,194						42,194
Cash dividends declared on common stock	(56,910)					(56,910)
Dividends on preferred stock	(8,200)					(8,200)
Stock-based compensation	11,304			11,304
Common stock issued for:
Acquisitions	71,756		1,074	70,682
Exercise of stock options and warrants	4,843		146	5,541	(844)
Restricted stock awards	(453)		150	(150)	(453)
Employee stock purchase plan	2,819		44	2,775
Director compensation plan	2,161		19	2,142
Balance at end of period at Dec. 31, 2019	$ 3,691,250	$ 125,000	$ 57,951	$ 1,650,278	$ (6,931)	$ 1,899,630	$ (34,678)