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)
Balance at at Dec. 31, 2015	$ 524,427		$ 24,296	$ 175,588	$ 325,840	$ (1,297)
Net income	10,813		0	0	10,813	0
Other comprehensive income (loss), net of tax	5,530		0	0	0	5,530
Common stock dividends - $0.26 and $0.24 per share at March 31, 2017 and 2016, respectively	(5,843)		0	0	(5,843)	0
Stock compensation expense, Adjustments to Additional Paid in Capital, Requisite Service Period Recognition, Total	477		0	477	0	0
Common stock issued pursuant to:
Stock option plan - 17,362 and 21,694 shares at March 31, 2017 and 2016, respectively	285		21	264	0	0
Employee stock purchase plan - 4,431 and 6,937 shares at March 31, 2017 and 2016, respectively	157		7	150	0	0
Restricted stock - 7,288 and 15,162 shares at March 31, 2017 and 2016, respectively	(181)		15	(196)	0	0
Purchase of treasury shares - 512,459 shares at March 31, 2016	(13,273)	$ (512)		(12,761)	0	0
Balance at at Mar. 31, 2016	522,392		23,827	163,522	330,810	4,233
Balance at at Dec. 31, 2016	533,572		23,901	165,871	350,414	(6,614)
Net income	15,112		0	0	15,112	0
Other comprehensive income (loss), net of tax	1,080		0	0	0	1,080
Common stock dividends - $0.26 and $0.24 per share at March 31, 2017 and 2016, respectively	(6,275)		0	0	(6,275)	0
Stock compensation expense, Adjustments to Additional Paid in Capital, Requisite Service Period Recognition, Total	496		0	496	0	0
Common stock issued pursuant to:
Stock option plan - 17,362 and 21,694 shares at March 31, 2017 and 2016, respectively	300		17	283	0	0
Employee stock purchase plan - 4,431 and 6,937 shares at March 31, 2017 and 2016, respectively	156		5	151	0	0
Restricted stock - 7,288 and 15,162 shares at March 31, 2017 and 2016, respectively	(180)		7	(187)	0	0
Balance at at Mar. 31, 2017	$ 544,261		$ 23,930	$ 166,614	$ 359,251	$ (5,534)