Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2017	$ 425,423	$ 204	$ 210,081	$ (22,370)	$ 233,896	$ 3,612
Beginning Balance (ASU 2018-02 [Member]) at Dec. 31, 2017					(414)	414
Beginning Balance (ASU 2016-01 [Member]) at Dec. 31, 2017					615	(615)
Beginning Balance, Shares at Dec. 31, 2017		20,504,165
Treasury Stock Beginning Balance, Shares at Dec. 31, 2017				(1,258,250)
Comprehensive income:
Net income	71,632				71,632
Other comprehensive income:
Change in unrealized gains loss, net of tax	(4,243)					(4,243)
Comprehensive income	67,389
Common stock issued upon exercise of options	67		67
Common stock issued upon exercise of options, Shares		15,000
Common stock issued	196	$ 1	195
Common stock issued, Shares		9,065
Share-based compensation	1,088		1,088
Dividends to shareholders	(84,401)				(84,401)
Ending Balance at Dec. 31, 2018	409,762	$ 205	211,431	$ (22,370)	221,328	(832)
Ending Balance (ASU 2016-02 [Member]) at Dec. 31, 2018	(1)				(1)
Ending Balance, Shares at Dec. 31, 2018		20,528,230
Treasury Stock Ending Balance, Shares at Dec. 31, 2018				(1,258,250)
Comprehensive income:
Net income	92,690				92,690
Other comprehensive income:
Change in unrealized gains loss, net of tax	13,043					13,043
Comprehensive income	105,733
Common stock issued upon exercise of options	20		20
Common stock issued upon exercise of options, Shares		5,000
Common stock issued	560		560
Common stock issued, Shares		27,603
Share-based compensation	993		993
Dividends to shareholders	(86,852)				(86,852)
Ending Balance at Dec. 31, 2019	430,215	$ 205	213,004	$ (22,370)	227,165	12,211
Ending Balance (ASU 2016-13 [Member]) at Dec. 31, 2019	$ (594)				(594)
Ending Balance, Shares at Dec. 31, 2019	19,302,583	20,560,833
Treasury Stock Ending Balance, Shares at Dec. 31, 2019	(1,258,250)			(1,258,250)
Comprehensive income:
Net income	$ 86,602				86,602
Other comprehensive income:
Change in unrealized gains loss, net of tax	8,808					8,808
Comprehensive income	95,410
Common stock issued	1,360	$ 1	1,359
Common stock issued, Shares		28,476
Share-based compensation	953		953
Dividends to shareholders	(88,528)				(88,528)
Ending Balance at Dec. 31, 2020	$ 438,816	$ 206	$ 215,316	$ (22,370)	$ 224,645	$ 21,019
Ending Balance, Shares at Dec. 31, 2020	19,331,059	20,589,309
Treasury Stock Ending Balance, Shares at Dec. 31, 2020	(1,258,250)			(1,258,250)