Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Deferred Benefits for Directors [Member]
Beginning Balance at Dec. 31, 2017	$ 1,395,321	$ 91,756	$ 684,730	$ 651,357		$ (31,495)	$ (1,027)
Beginning Balance, shares at Dec. 31, 2017		44,043,244
Net income	66,698			66,698
Other Comprehensive Income (Loss)	(20,794)					(20,794)
Comprehensive income	45,904
Common dividends declared	(26,298)			(26,298)
Adoption of accounting standard ASU 2016-01				1,063		(1,063)
Shares issued for acquisition	107,347	$ 5,206	102,141
Shares issued for acquisition, shares		2,498,761
Treasury shares acquired	(680)		34		$ (714)
Treasury shares acquired, shares		(15,159)
Stock options exercised	1,143	$ 69	915		159
Stock options exercised, shares		36,788
Restricted stock granted		$ 166	(166)
Restricted stock granted, shares		79,616
Stock compensation expense	1,838		1,838
Deferred benefits for directors- net	(469)		(454)				(15)
Ending Balance at Jun. 30, 2018	1,524,106	$ 97,197	789,038	692,820	(555)	(53,352)	(1,042)
Ending Balance, shares at Jun. 30, 2018		46,643,250
Beginning Balance at Mar. 31, 2018	1,403,026	$ 91,793	686,169	673,174		(47,076)	(1,034)
Beginning Balance, shares at Mar. 31, 2018		44,060,957
Net income	33,169			33,169
Other Comprehensive Income (Loss)	(6,276)					(6,276)
Comprehensive income	26,893
Common dividends declared	(13,523)			(13,523)
Shares issued for acquisition	107,347	$ 5,206	102,141
Shares issued for acquisition, shares		2,498,761
Treasury shares acquired	(680)		34		(714)
Treasury shares acquired, shares		(15,159)
Stock options exercised	583	$ 32	392		159
Stock options exercised, shares		19,075
Restricted stock granted		$ 166	(166)
Restricted stock granted, shares		79,616
Stock compensation expense	929		929
Deferred benefits for directors- net	(469)		(461)				(8)
Ending Balance at Jun. 30, 2018	1,524,106	$ 97,197	789,038	692,820	(555)	(53,352)	(1,042)
Ending Balance, shares at Jun. 30, 2018		46,643,250
Beginning Balance at Dec. 31, 2018	1,978,827	$ 113,758	1,166,701	737,581	(274)	(37,871)	(1,068)
Beginning Balance, shares at Dec. 31, 2018		54,598,134
Net income	85,151			85,151
Other Comprehensive Income (Loss)	41,984					41,984
Comprehensive income	127,135
Common dividends declared	(33,832)			(33,832)
Treasury shares acquired	(589)		128		(717)
Treasury shares acquired, shares		(19,385)
Stock options exercised	121	$ 8	12		101
Stock options exercised, shares		6,000
Restricted stock granted		$ 186	(1,074)		888
Restricted stock granted, shares		112,450
Stock compensation expense	2,439		2,439
Deferred benefits for directors- net	15		6				9
Ending Balance at Jun. 30, 2019	2,074,116	$ 113,952	1,168,212	788,900	(2)	4,113	(1,059)
Ending Balance, shares at Jun. 30, 2019		54,697,199
Beginning Balance at Mar. 31, 2019	2,023,139	$ 113,758	1,167,761	761,002	(229)	(18,098)	(1,055)
Beginning Balance, shares at Mar. 31, 2019		54,599,127
Net income	44,814			44,814
Other Comprehensive Income (Loss)	22,211					22,211
Comprehensive income	67,025
Common dividends declared	(16,916)			(16,916)
Treasury shares acquired	(589)		128		(717)
Treasury shares acquired, shares		(19,378)
Stock options exercised	101	$ 8	37		56
Stock options exercised, shares		5,000
Restricted stock granted		$ 186	(1,074)		888
Restricted stock granted, shares		112,450
Stock compensation expense	1,364		1,364
Deferred benefits for directors- net	(8)		(4)				(4)
Ending Balance at Jun. 30, 2019	$ 2,074,116	$ 113,952	$ 1,168,212	$ 788,900	$ (2)	$ 4,113	$ (1,059)
Ending Balance, shares at Jun. 30, 2019		54,697,199