Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - 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, 2018	$ 409,762	$ 205	$ 211,431	$ (22,370)	$ 221,328	$ (832)
Beginning Balance (ASU 2016-02 [Member]) at Dec. 31, 2018	(1)				(1)
Beginning Balance, Shares at Dec. 31, 2018		20,528,230		(1,258,250)
Comprehensive income:
Net income	58,676				58,676
Other comprehensive income:
Change in unrealized gains (losses), net of tax	13,447					13,447
Comprehensive income	72,123
Common stock issued upon exercise of options	$ 20		20
Common stock issued upon exercise of options, Shares	5,000	5,000
Common stock issued	$ 559		559
Common stock issued, Shares		25,329
Share-based compensation	733		733
Dividends to shareholders	(14,467)				(14,467)
Ending Balance at Sep. 30, 2019	468,729	$ 205	212,743	$ (22,370)	265,536	12,615
Ending Balance, Shares at Sep. 30, 2019		20,558,559		(1,258,250)
Beginning Balance at Jun. 30, 2019	449,443	$ 205	212,493	$ (22,370)	248,975	10,140
Beginning Balance, Shares at Jun. 30, 2019		20,556,511		(1,258,250)
Comprehensive income:
Net income	21,386				21,386
Other comprehensive income:
Change in unrealized gains (losses), net of tax	2,475					2,475
Comprehensive income	23,861
Common stock issued	(1)		(1)
Common stock issued, Shares		2,048
Share-based compensation	251		251
Dividends to shareholders	(4,825)				(4,825)
Ending Balance at Sep. 30, 2019	468,729	$ 205	212,743	$ (22,370)	265,536	12,615
Ending Balance, Shares at Sep. 30, 2019		20,558,559		(1,258,250)
Beginning Balance at Dec. 31, 2019	430,215	$ 205	213,004	$ (22,370)	227,165	12,211
Beginning Balance (ASU 2016-13 [Member]) at Dec. 31, 2019	$ (594)				(594)
Beginning Balance, Shares at Dec. 31, 2019	19,302,583	20,560,833		(1,258,250)
Comprehensive income:
Net income	$ 58,101				58,101
Other comprehensive income:
Change in unrealized gains (losses), net of tax	7,701					7,701
Comprehensive income	$ 65,802
Common stock issued upon exercise of options, Shares	0
Common stock issued	$ 1,360	$ 1	1,359
Common stock issued, Shares		28,476
Share-based compensation	777		777
Dividends to shareholders	(15,650)				(15,650)
Ending Balance at Sep. 30, 2020	$ 481,910	$ 206	215,140	$ (22,370)	269,022	19,912
Ending Balance, Shares at Sep. 30, 2020	19,331,059	20,589,309		(1,258,250)
Beginning Balance at Jun. 30, 2020	$ 462,796	$ 206	214,894	$ (22,370)	250,888	19,178
Beginning Balance, Shares at Jun. 30, 2020		20,589,309		(1,258,250)
Comprehensive income:
Net income	23,353				23,353
Other comprehensive income:
Change in unrealized gains (losses), net of tax	734					734
Comprehensive income	24,087
Share-based compensation	246		246
Dividends to shareholders	(5,219)				(5,219)
Ending Balance at Sep. 30, 2020	$ 481,910	$ 206	$ 215,140	$ (22,370)	$ 269,022	$ 19,912
Ending Balance, Shares at Sep. 30, 2020	19,331,059	20,589,309		(1,258,250)