Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income
Balance, beginning of year, shares at Dec. 31, 2018		1,887
Balance, beginning of year at Dec. 31, 2018	$ 175,639	$ 0	$ 174,690	$ 949
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	12,126		12,126
Dividends paid	(1,511)		(1,511)
Shares of common stock repurchased and retired (in shares)		0
Shares of common stock repurchased and retired	(11)		(11)
Stock options and stock appreciation rights exercised (in shares)		2
Stock options and stock appreciation rights exercised	0		0
Share-based compensation expense related to stock appreciation rights	147		147
Accumulated postretirement benefit obligation adjustment	0
Net unrealized gain on investments	1,905			1,905
Balance, end of year, shares at Jun. 30, 2019		1,889
Balance, end of year at Jun. 30, 2019	$ 188,295	$ 0	185,441	2,854
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.80
Balance, beginning of year, shares at Mar. 31, 2019		1,889
Balance, beginning of year at Mar. 31, 2019	$ 182,729	$ 0	180,637	2,092
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,500		5,500
Dividends paid	(756)		(756)
Stock options and stock appreciation rights exercised (in shares)		0
Stock options and stock appreciation rights exercised	1		1
Share-based compensation expense related to stock appreciation rights	59		59
Net unrealized gain on investments	762			762
Balance, end of year, shares at Jun. 30, 2019		1,889
Balance, end of year at Jun. 30, 2019	$ 188,295	$ 0	185,441	2,854
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.40
Balance, beginning of year, shares at Dec. 31, 2019		1,889
Balance, beginning of year at Dec. 31, 2019	$ 191,362	$ 0	188,262	3,100
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,484		7,484
Dividends paid	(1,664)		(1,664)
Stock options and stock appreciation rights exercised (in shares)		3
Stock options and stock appreciation rights exercised	(1)		(1)
Share-based compensation expense related to stock appreciation rights	154		154
Accumulated postretirement benefit obligation adjustment	(32)			(32)
Net unrealized gain on investments	1,162			1,162
Balance, end of year, shares at Jun. 30, 2020		1,892
Balance, end of year at Jun. 30, 2020	$ 198,465	$ 0	194,235	4,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.88
Balance, beginning of year, shares at Mar. 31, 2020		1,891
Balance, beginning of year at Mar. 31, 2020	$ 183,647	$ 0	180,535	3,112
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,495		14,495
Dividends paid	(832)		(832)
Stock options and stock appreciation rights exercised (in shares)		1
Stock options and stock appreciation rights exercised	0		0
Share-based compensation expense related to stock appreciation rights	37		37
Net unrealized gain on investments	1,118			1,118
Balance, end of year, shares at Jun. 30, 2020		1,892
Balance, end of year at Jun. 30, 2020	$ 198,465	$ 0	$ 194,235	$ 4,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.44