CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Class A Common Stock	Class B Common Stock	Total
Balance at Dec. 31, 2017	$ 62,675	$ 151,608	$ (34,894)	$ 67	$ 9	$ 179,465
Balance, shares at Dec. 31, 2017				6,694	898
Net income		1,529				1,529
Issuance of restricted stock (in shares)				4
Dividends declared per common share		(1,784)				(1,784)
Compensation expense related to restricted stock awards	551					551
Purchase of shares held in treasury			(93)			(93)
401(k) plan contribution	(80)		333			253
Balance at Mar. 31, 2018	63,146	151,353	(34,654)	$ 67	$ 9	179,921
Balance, shares at Mar. 31, 2018				6,698	898
Balance at Dec. 31, 2017	62,675	151,608	(34,894)	$ 67	$ 9	179,465
Balance, shares at Dec. 31, 2017				6,694	898
Net income						9,395
Balance at Sep. 30, 2018	64,270	155,668	(35,856)	$ 67	$ 9	184,158
Balance, shares at Sep. 30, 2018				6,697	898
Balance at Dec. 31, 2017	62,675	151,608	(34,894)	$ 67	$ 9	179,465
Balance, shares at Dec. 31, 2017				6,694	898
Issuance of restricted stock (in shares)				27	37
Forfeiture of restricted stock (in shares)				(1)	0
Balance at Dec. 31, 2018	64,795	156,689	(36,561)	$ 67	$ 9	184,999
Balance, shares at Dec. 31, 2018				6,732	923
Balance at Mar. 31, 2018	63,146	151,353	(34,654)	$ 67	$ 9	179,921
Balance, shares at Mar. 31, 2018				6,698	898
Net income		4,171				4,171
Forfeiture of restricted stock (in shares)				(1)
Dividends declared per common share		(1,777)				(1,777)
Compensation expense related to restricted stock awards	553					553
Purchase of shares held in treasury			(454)			(454)
Balance at Jun. 30, 2018	63,699	153,747	(35,108)	$ 67	$ 9	182,414
Balance, shares at Jun. 30, 2018				6,697	898
Net income		3,695				3,695
Dividends declared per common share		(1,774)				(1,774)
Compensation expense related to restricted stock awards	571					571
Purchase of shares held in treasury			(748)			(748)
Balance at Sep. 30, 2018	64,270	155,668	(35,856)	$ 67	$ 9	184,158
Balance, shares at Sep. 30, 2018				6,697	898
Balance at Dec. 31, 2018	64,795	156,689	(36,561)	$ 67	$ 9	184,999
Balance, shares at Dec. 31, 2018				6,732	923
Net income		1,370				1,370
Dividends declared per common share		(1,784)				(1,784)
Compensation expense related to restricted stock awards	559					559
Purchase of shares held in treasury			(80)			(80)
401(k) plan contribution	(113)		375			262
Balance at Mar. 31, 2019	65,241	156,275	(36,266)	$ 67	$ 9	185,326
Balance, shares at Mar. 31, 2019				6,732	923
Balance at Dec. 31, 2018	64,795	156,689	(36,561)	$ 67	$ 9	184,999
Balance, shares at Dec. 31, 2018				6,732	923
Net income						9,438
Forfeiture of restricted stock (in shares)				(2)
Balance at Sep. 30, 2019	66,338	160,778	(36,789)	$ 67	$ 9	190,403
Balance, shares at Sep. 30, 2019				6,730	923
Balance at Mar. 31, 2019	65,241	156,275	(36,266)	$ 67	$ 9	185,326
Balance, shares at Mar. 31, 2019				6,732	923
Net income		4,734				4,734
Dividends declared per common share		(1,784)				(1,784)
Compensation expense related to restricted stock awards	565					565
Purchase of shares held in treasury			(247)			(247)
Balance at Jun. 30, 2019	65,806	159,225	(36,513)	$ 67	$ 9	188,594
Balance, shares at Jun. 30, 2019				6,732	923
Net income		3,334				3,334
Forfeiture of restricted stock (in shares)				(2)
Dividends declared per common share		(1,781)				(1,781)
Compensation expense related to restricted stock awards	532					532
Purchase of shares held in treasury			(276)			(276)
Balance at Sep. 30, 2019	$ 66,338	$ 160,778	$ (36,789)	$ 67	$ 9	$ 190,403
Balance, shares at Sep. 30, 2019				6,730	923