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, 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	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
Balance at Dec. 31, 2016	99,214	171,425	201,517	(6,251)	(33,219)	432,686
Net income	0	0	35,783	0	0	35,783
Other comprehensive income, net of tax	0	0	0	3,191	0	3,191
Cash dividend declared	0	0	(18,899)	0	0	(18,899)
Stock options exercised	348	1,510	0	0	0	1,858
Purchase of treasury stock	0	0	0	0	(1,683)	(1,683)
Sale of treasury stock	0	(337)	0	0	2,215	1,878
Stock based compensation expense	0	114	0	0	0	114
Balance at Sep. 30, 2017	99,562	172,712	218,401	(3,060)	(32,687)	454,928
Balance at Jun. 30, 2017				(3,593)
Net income						12,596
Other comprehensive income, net of tax						533
Balance at Sep. 30, 2017	$ 99,562	$ 172,712	$ 218,401	$ (3,060)	$ (32,687)	$ 454,928