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, 2014	$ 115,245	$ 64	$ 8	$ 52,496	$ 91,178	$ (28,501)
Balance, shares at Dec. 31, 2014		6,446	843
Net income	13,414				13,414
Conversion of shares from Class B to Class A	0	$ 1	$ (1)
Conversion of shares from Class B to Class A (in shares)		40	(40)
Issuance of restricted stock	0	$ 0	$ 0
Issuance of restricted stock (in shares)		26	30
Forfeiture of restricted stock	0	$ 0
Forfeiture of restricted stock (in shares)		(2)
Net proceeds from exercised options	(767)	$ 1	$ 1	3,393		(4,162)
Net proceeds from exercised options (in shares)		93	32
Dividends declared per common share	(6,412)				(6,412)
Compensation expense related to restricted stock awards	1,655			1,655
Purchase of shares held in treasury	(563)					(563)
401(k) plan contribution	244			(34)		278
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
Conversion of shares from Class B to Class A (in shares)		12	(12)
Issuance of restricted stock	0	$ 0	$ 0
Issuance of restricted stock (in shares)		23	25
Dividends declared per common share	(7,633)				(7,633)
Compensation expense related to restricted stock awards	2,101			2,101
Purchase of shares held in treasury	(746)					(746)
401(k) plan contribution	258			(54)		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
Conversion of shares from Class B to Class A (in shares)		17	(17)
Issuance of restricted stock	0	$ 0	$ 1	(1)
Issuance of restricted stock (in shares)		19	29
Forfeiture of restricted stock	0	$ 0
Forfeiture of restricted stock (in shares)		(1)
Net proceeds from exercised options	1	$ 1	$ 0	826		(826)
Net proceeds from exercised options (in shares)		21	8
Dividends declared per common share	(11,842)				(11,842)
Compensation expense related to restricted stock awards	2,279			2,279
Purchase of shares held in treasury	(946)					(946)
401(k) plan contribution	274			14		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