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	20,078		20,078
Dividends paid	(2,266)		(2,266)
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	204		204
Accumulated postretirement benefit obligation adjustment	0
Net unrealized gain on investments	2,246			2,246
Other	0
Balance, end of year, shares at Sep. 30, 2019		1,889
Balance, end of year at Sep. 30, 2019	$ 195,890	$ 0	192,695	3,195
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 1.20
Balance, beginning of year, shares at Jun. 30, 2019		1,889
Balance, beginning of year at Jun. 30, 2019	$ 188,295	$ 0	185,441	2,854
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,952		7,952
Dividends paid	(755)		(755)
Stock options and stock appreciation rights exercised (in shares)		0
Stock options and stock appreciation rights exercised	0		0
Share-based compensation expense related to stock appreciation rights	57		57
Net unrealized gain on investments	341			341
Balance, end of year, shares at Sep. 30, 2019		1,889
Balance, end of year at Sep. 30, 2019	$ 195,890	$ 0	192,695	3,195
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	22,785		22,785
Dividends paid	(2,497)		(2,497)
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	192		192
Accumulated postretirement benefit obligation adjustment	(32)			(32)
Net unrealized gain on investments	1,212			1,212
Other	(94)		(94)
Balance, end of year, shares at Sep. 30, 2020		1,892
Balance, end of year at Sep. 30, 2020	$ 212,927	$ 0	208,647	4,280
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 1.32
Balance, beginning of year, shares at Jun. 30, 2020		1,892
Balance, beginning of year at Jun. 30, 2020	$ 198,465	$ 0	194,235	4,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,301		15,301
Dividends paid	(833)		(833)
Stock options and stock appreciation rights exercised (in shares)		0
Stock options and stock appreciation rights exercised	0		0
Share-based compensation expense related to stock appreciation rights	38		38
Net unrealized gain on investments	50			50
Other	(94)		(94)
Balance, end of year, shares at Sep. 30, 2020		1,892
Balance, end of year at Sep. 30, 2020	$ 212,927	$ 0	$ 208,647	$ 4,280
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.44