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	39,052					39,052
Other comprehensive income, net of tax	6,241						6,241
Cash dividends declared on common stock	(5,202)					(5,202)
Dividends on preferred stock	(1,581)					(1,581)
Stock-based compensation	2,271			2,271	0
Conversion of Series C preferred stock to common stock	0	(40)	1	39
Common stock issued for:
Acquisitions	19,004		422	18,582
Exercise of stock options and warrants	457		52	535	(130)
Restricted stock awards	144		84	329	(269)
Employee stock purchase plan	681		15	666
Director compensation plan	185		20	165
Balance at Mar. 31, 2015	2,131,074	126,427	47,475	1,156,542	(3,948)	835,669	(31,091)
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	49,111					49,111	0
Other comprehensive income, net of tax	22,798						22,798
Cash dividends declared on common stock	(5,812)					(5,812)
Dividends on preferred stock	(3,628)					(3,628)
Stock-based compensation	2,484			2,484
Conversion of Series C preferred stock to common stock	0	(30)	1	29
Common stock issued for:
Exercise of stock options and warrants	141		17	124	0
Restricted stock awards	16		82	106	(172)
Employee stock purchase plan	648		14	634
Director compensation plan	410		25	385
Balance at Mar. 31, 2016	$ 2,418,442	$ 251,257	$ 48,608	$ 1,194,750	$ (4,145)	$ 967,882	$ (39,910)