Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2015	$ 122,816	$ 66	$ 8	$ 57,510	$ 98,180	$ (32,948)
Balance, shares at Dec. 31, 2015		6,603	865
Net income	18,186				18,186
Conversion of shares from Class B to Class A	0	$ 0	$ 0	0	0	0
Conversion of shares from Class B to Class A (in shares)		12	(12)
Issuance of restricted stock	0	$ 0	$ 0	0	0	0
Issuance of restricted stock (in shares)		23	25
Dividends declared per common share	(7,633)	$ 0	$ 0	0	(7,633)	0
Compensation expense related to restricted stock awards	2,101	0	0	2,101	0	0
Purchase of shares held in treasury	(746)	0	0	0	0	(746)
401(k) plan contribution	258	0	0	(54)	0	312
Balance at Dec. 31, 2016	134,982	$ 66	$ 8	59,557	108,733	(33,382)
Balance, shares at Dec. 31, 2016		6,638	878
Net income	54,717				54,717
Conversion of shares from Class B to Class A	0	$ 0	$ 0		0	0
Conversion of shares from Class B to Class A (in shares)		17	(17)
Issuance of restricted stock	0	$ 0	$ 1	(1)	0	0
Issuance of restricted stock (in shares)		19	29
Forfeiture of restricted stock	0	$ 0			0	0
Forfeiture of restricted stock (in shares)		(1)
Net proceeds from exercised options	1	$ 1	$ 0	826	0	(826)
Net proceeds from exercised options (in shares)		21	8
Dividends declared per common share	(11,842)	$ 0	$ 0		(11,842)
Compensation expense related to restricted stock awards	2,279	0	0	2,279	0	0
Purchase of shares held in treasury	(946)	0	0		0	(946)
401(k) plan contribution	274	0	0	14	0	260
Balance at Dec. 31, 2017	179,465	$ 67	$ 9	62,675	151,608	(34,894)
Balance, shares at Dec. 31, 2017		6,694	898
Net income	13,690				13,690
Conversion of shares from Class B to Class A	0	$ 0	$ 0	0	0	0
Conversion of shares from Class B to Class A (in shares)		12	(12)
Issuance of restricted stock	0	$ 0	$ 0	0	0	0
Issuance of restricted stock (in shares)		27	37
Forfeiture of restricted stock	0	$ 0	$ 0
Forfeiture of restricted stock (in shares)		(1)
Dividends declared per common share	(8,609)	$ 0	0		(8,609)
Compensation expense related to restricted stock awards	2,201	0	0	2,201
Purchase of shares held in treasury	(2,000)	0	0			(2,000)
401(k) plan contribution	252	0	0	(81)		333
Balance at Dec. 31, 2018	$ 184,999	$ 67	$ 9	$ 64,795	$ 156,689	$ (36,561)
Balance, shares at Dec. 31, 2018		6,732	923