Consolidated Statements Of Changes In Shareholders Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Accumulated other comprehensive loss
Balance at Dec. 31, 2013	$ 1,900,589	$ 126,477	$ 46,181	$ 1,117,032	$ (3,000)	$ 676,935	$ (63,036)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	34,500					34,500
Other comprehensive income, net of tax	6,283						6,283
Cash dividends declared on common stock	(4,620)					(4,620)
Dividends on preferred stock	(1,581)					(1,581)
Stock-based compensation	1,681			1,681	0
Common stock issued for:
Exercise of stock options and warrants	2,270		77	2,464	(271)
Restricted stock awards	43		41	111	(109)
Employee stock purchase plan	600		13	587
Director compensation plan	378		20	358
Balance at Mar. 31, 2014	1,940,143	126,477	46,332	1,122,233	(3,380)	705,234	(56,753)
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	0
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
Conversion of Series C preferred stock to common stock	0	(40)	1	39
Common stock issued for:
Acquisitions	19,004		422	18,582	0
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)