Consolidated Statements Of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive loss
Balance at Dec. 31, 2014	$ 2,069,822	$ 126,467	$ 46,881	$ 1,133,955	$ (3,549)	$ 803,400	$ (37,332)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	121,238					121,238
Other comprehensive income (loss), net of tax	(11,761)						(11,761)
Cash dividends declared on common stock	(15,746)					(15,746)
Dividends on preferred stock	(7,240)					(7,240)
Stock-based compensation	7,817			7,817
Issuance of stock	120,842	125,000		(4,158)
Conversion of Series C preferred stock to common stock	0	(155)	4	151
Common stock issued for:
Acquisitions	38,723		811	37,912
Exercise of stock options and warrants	8,575		564	8,141	(130)
Restricted stock awards	196		99	382	(285)
Employee stock purchase plan	2,040		43	1,997
Director compensation plan	1,230		20	1,210
Balance at Sep. 30, 2015	2,335,736	251,312	48,422	1,187,407	(3,964)	901,652	(49,093)
Balance at Dec. 31, 2015	2,352,274	251,287	48,469	1,190,988	(3,973)	928,211	(62,708)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	152,267					152,267
Other comprehensive income (loss), net of tax	30,129						30,129
Cash dividends declared on common stock	(17,846)					(17,846)
Dividends on preferred stock	(10,884)					(10,884)
Stock-based compensation	6,778			6,778
Issuance of stock	152,823		3,000	149,823
Conversion of Series C preferred stock to common stock	0	(30)	1	29
Common stock issued for:
Exercise of stock options and warrants	5,773		185	5,965	(377)
Restricted stock awards	37		88	121	(172)
Employee stock purchase plan	1,933		43	1,890
Director compensation plan	1,190		25	1,165
Balance at Sep. 30, 2016	$ 2,674,474	$ 251,257	$ 51,811	$ 1,356,759	$ (4,522)	$ 1,051,748	$ (32,579)