CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid- In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2018	$ 12	$ 8,802	$ (173)	$ 131,344	$ (30,879)	$ 109,106
Balance (in shares) at Dec. 31, 2018	12,117
Net income				20,750		20,750
Share-based compensation		990				990
Options exercised by executives and directors		269				269
Options exercised by executives and directors (in shares)	10
Net shares repurchased for employee taxes		(256)				(256)
Net shares repurchased for employee taxes, (in shares)	(1)
Other comprehensive income			127			127
Cash dividends declared to stockholders				(8,918)		(8,918)
Balance at Mar. 31, 2019	$ 12	9,805	(46)	143,176	(30,879)	122,068
Balance (in shares) at Mar. 31, 2019	12,126
Balance at Dec. 31, 2018	$ 12	8,802	(173)	131,344	(30,879)	109,106
Balance (in shares) at Dec. 31, 2018	12,117
Net income						$ 58,035
Net shares repurchased for employee taxes, (in shares)						(0)
Other comprehensive income						$ 245
Balance at Sep. 30, 2019	$ 12	12,207	72	162,902	(63,993)	111,200
Balance (in shares) at Sep. 30, 2019	12,126
Balance at Mar. 31, 2019	$ 12	9,805	(46)	143,176	(30,879)	122,068
Balance (in shares) at Mar. 31, 2019	12,126
Net income				21,383		21,383
Share-based compensation		1,255				1,255
Options exercised by executives and directors		10				10
Other comprehensive income			102			102
Treasury stock from stock repurchases					(9,998)	(9,998)
Cash dividends declared to stockholders				(8,797)		(8,797)
Balance at Jun. 30, 2019	$ 12	11,070	56	155,762	(40,877)	126,023
Balance (in shares) at Jun. 30, 2019	12,126
Net income				15,902		15,902
Share-based compensation		1,170				1,170
Net shares repurchased for employee taxes		(33)				(33)
Other comprehensive income			16			16
Treasury stock from stock repurchases					(23,116)	(23,116)
Cash dividends declared to stockholders				(8,762)		(8,762)
Balance at Sep. 30, 2019	$ 12	12,207	72	162,902	(63,993)	111,200
Balance (in shares) at Sep. 30, 2019	12,126
Balance at Dec. 31, 2019	$ 12		25	168,788	(63,993)	104,832
Balance (in shares) at Dec. 31, 2019	12,272
Net income				18,477		18,477
Share-based compensation		981				981
Share-based compensation (in shares)	7
Net shares repurchased for employee taxes		(487)				(487)
Net shares repurchased for employee taxes, (in shares)	(5)
Other comprehensive income			45			45
Treasury stock retired from stock repurchases				(63,993)	63,993
Treasury stock retired from stock repurchases, (in shares)	(489)
Cash dividends declared to stockholders				(13,099)		(13,099)
Balance at Mar. 31, 2020	$ 12	494	70	110,173		110,749
Balance (in shares) at Mar. 31, 2020	11,785
Balance at Dec. 31, 2019	$ 12		25	168,788	(63,993)	104,832
Balance (in shares) at Dec. 31, 2019	12,272
Net income						$ 74,865
Net shares repurchased for employee taxes, (in shares)						(0)
Other comprehensive income						$ 72
Balance at Sep. 30, 2020	$ 12	5,135	97	139,770	(5,000)	140,014
Balance (in shares) at Sep. 30, 2020	11,817
Balance at Mar. 31, 2020	$ 12	494	70	110,173		110,749
Balance (in shares) at Mar. 31, 2020	11,785
Net income				21,935		21,935
Share-based compensation		1,136				1,136
Options exercised by executives and directors		1,250				1,250
Options exercised by executives and directors (in shares)	21
Net shares repurchased for employee taxes		(9)				(9)
Other comprehensive income			29			29
Treasury stock from stock repurchases					(5,000)	(5,000)
Cash dividends declared to stockholders				(13,354)		(13,354)
Balance at Jun. 30, 2020	$ 12	2,871	99	118,754	(5,000)	116,736
Balance (in shares) at Jun. 30, 2020	11,806
Net income				34,453		34,453
Share-based compensation		2,126				2,126
Share-based compensation (in shares)	9
Options exercised by executives and directors		174				174
Options exercised by executives and directors (in shares)	2
Net shares repurchased for employee taxes		(36)				(36)
Other comprehensive income			(2)			(2)
Cash dividends declared to stockholders				(13,437)		(13,437)
Balance at Sep. 30, 2020	$ 12	$ 5,135	$ 97	$ 139,770	$ (5,000)	$ 140,014
Balance (in shares) at Sep. 30, 2020	11,817