CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock Outstanding [Member]	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balances at Dec. 31, 2013	$ 499,363		$ 24,990	$ 193,445	$ 283,898	$ (2,970)
Net income	38,200		0	0	38,200	0
Other comprehensive loss, net of tax	2,147		0	0	0	2,147
Common stock dividends - $0.72 and $0.66 per share at September 30, 2016 and 2015, respectively	(19,216)		0	0	(19,216)	0
Stock compensation expense, Adjustments to Additional Paid in Capital, Requisite Service Period Recognition, Total	1,773		0	1,773	0	0
Common stock issued pursuant to:
Stock option plan - 34,646 and 35,039 shares at September 30, 2016 and 2015, respectively	190		14	176	0	0
Employee stock purchase plan - 18,767 and 19,377 shares at September 30, 2016 and 2015, respectively	509		25	484	0	0
Restricted stock - 49,648 and 53,746 shares at September 30, 2016 and 2015, respectively	(305)		54	(359)	0	0
Purchase of treasury shares - 512,459 and 728,932 shares at September 30, 2016 and 2015, respectively	(910)	$ (38)		(872)	0	0
Balances at Dec. 31, 2014	521,751		25,045	194,647	302,882	(823)
Net income	45,355		0	0	45,355	0
Other comprehensive loss, net of tax	(474)		0	0	0	(474)
Common stock dividends - $0.72 and $0.66 per share at September 30, 2016 and 2015, respectively	(22,397)		0	0	(22,397)	0
Stock compensation expense, Adjustments to Additional Paid in Capital, Requisite Service Period Recognition, Total	1,979		0	1,979	0	0
Common stock issued pursuant to:
Stock option plan - 34,646 and 35,039 shares at September 30, 2016 and 2015, respectively	602		40	562	0	0
Directors stock purchase plan - 258 and 837 shares at September 30, 2016 and 2015, respectively	22		1	21	0	0
Employee stock purchase plan - 18,767 and 19,377 shares at September 30, 2016 and 2015, respectively	566		25	541	0	0
Restricted stock - 49,648 and 53,746 shares at September 30, 2016 and 2015, respectively	(353)		56	(409)	0	0
Purchase of treasury shares - 512,459 and 728,932 shares at September 30, 2016 and 2015, respectively	(22,624)	(871)		(21,753)	0	0
Balances at Dec. 31, 2015	524,427		24,296	175,588	325,840	(1,297)
Net income	48,250		0	0	48,250	0
Other comprehensive loss, net of tax	(5,317)		0	0	0	(5,317)
Common stock dividends - $0.72 and $0.66 per share at September 30, 2016 and 2015, respectively	(23,676)		0	0	(23,676)	0
Stock compensation expense, Adjustments to Additional Paid in Capital, Requisite Service Period Recognition, Total	2,264		0	2,264	0	0
Common stock issued pursuant to:
Stock option plan - 34,646 and 35,039 shares at September 30, 2016 and 2015, respectively	716		44	672	0	0
Directors stock purchase plan - 258 and 837 shares at September 30, 2016 and 2015, respectively	7		0	7	0	0
Employee stock purchase plan - 18,767 and 19,377 shares at September 30, 2016 and 2015, respectively	591		24	567	0	0
Restricted stock - 49,648 and 53,746 shares at September 30, 2016 and 2015, respectively	(417)		49	(466)	0	0
Purchase of treasury shares - 512,459 and 728,932 shares at September 30, 2016 and 2015, respectively	(13,273)	$ (512)		(12,761)	0	0
Balances at Dec. 31, 2016	$ 533,572		$ 23,901	$ 165,871	$ 350,414	$ (6,614)