Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income	Noncontrolling Interest [Member]
Balance, beginning of year at Dec. 31, 2016	$ 155,136	$ 0	$ 143,284	$ 11,761	$ 91
Balance, beginning of year, shares at Dec. 31, 2016		1,884
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the Company	10,151		10,151
Dividends paid	(1,038)		(1,038)
Shares of common stock repurchased and retired (in shares)		0
Shares of common stock repurchased and retired	(9)		(9)
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	95		95
Amortization related to postretirement health benefits	3			3
Net unrealized gain (loss) on investments	1,904			1,904
Net loss attributable to noncontrolling interests	(11)				(11)
Balance, end of year at Jun. 30, 2017	166,230	$ 0	152,482	13,668	80
Balance, end of year, shares at Jun. 30, 2017		1,887
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for adoption of new accounting standards	0		13,627	(13,627)
Balance, beginning of year at Dec. 31, 2017	177,921	$ 0	161,891	15,945	85
Balance, beginning of year, shares at Dec. 31, 2017		1,886
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to the Company	11,123		11,123
Dividends paid	(1,509)		(1,509)
Shares of common stock repurchased and retired (in shares)		0
Shares of common stock repurchased and retired	(29)		(29)
Stock options and stock appreciation rights exercised (in shares)		1
Stock options and stock appreciation rights exercised	(1)		(1)
Share-based compensation expense related to stock appreciation rights	150		150
Net unrealized gain (loss) on investments	(1,512)			(1,512)
Net loss attributable to noncontrolling interests	(30)				(30)
Balance, end of year at Jun. 30, 2018	$ 186,113	$ 0	$ 185,252	$ 806	$ 55
Balance, end of year, shares at Jun. 30, 2018		1,887