Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Capital Stock [Member]	Surplus [Member]	Undivided Profits [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2014	$ 98,945	$ 172,353	$ 166,745	$ (4,509)	$ (40,090)	$ 393,444
Net income	0	0	32,058	0	0	32,058
Other comprehensive income, net of tax	0	0	0	3,335	0	3,335
Cash dividend declared	0	0	(18,710)	0	0	(18,710)
Stock options exercised and related tax benefits	19	80	0	0	0	99
Purchase of treasury stock	0	0	0	0	(99)	(99)
Sale of treasury stock	0	(789)	0	0	2,810	2,021
Stock based compensation expense	0	144	0	0	0	144
Balance at Sep. 30, 2015	98,964	171,788	180,093	(1,174)	(37,379)	412,292
Balance at Jun. 30, 2015				(5,927)
Net income						10,616
Other comprehensive income, net of tax						4,753
Balance at Sep. 30, 2015	98,964	171,788	180,093	(1,174)	(37,379)	412,292
Balance at Dec. 31, 2015	98,973	171,443	184,009	(4,781)	(36,334)	413,310
Net income	0	0	31,803	0	0	31,803
Other comprehensive income, net of tax	0	0	0	7,109	0	7,109
Cash dividend declared	0	0	(18,799)	0	0	(18,799)
Stock options exercised and related tax benefits	148	612	0	0	0	760
Purchase of treasury stock	0	0	0	0	(701)	(701)
Sale of treasury stock	0	(1,130)	0	0	3,088	1,958
Stock based compensation expense	0	168	0	0	0	168
Balance at Sep. 30, 2016	99,121	171,093	197,013	2,328	(33,947)	435,608
Balance at Jun. 30, 2016				2,395
Net income						10,930
Other comprehensive income, net of tax						(67)
Balance at Sep. 30, 2016	$ 99,121	$ 171,093	$ 197,013	$ 2,328	$ (33,947)	$ 435,608