CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Scenario, Previously Reported [Member] Common Stock [Member]	Scenario, Previously Reported [Member] Additional Paid- In Capital [Member]	Scenario, Previously Reported [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Scenario, Previously Reported [Member] Retained Earnings [Member]	Scenario, Previously Reported [Member]	Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Retained Earnings [Member]	Difference between Revenue Guidance in Effect before and after Topic 606 [Member]	Common Stock [Member]	Additional Paid- In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Cumulative effect adjustments from changes in accounting standards						$ (2,018)	$ (2,018)
Balance at Dec. 31, 2017	$ 12	$ 4,967	$ (160)	$ 103,762	$ 108,581			$ 12	$ 4,967	$ (160)	$ 101,744		$ 106,563
Balance (in shares) at Dec. 31, 2017	12,103							12,103
Net income											12,222		12,222
Share-based compensation									805				805
Share-based compensation (in shares)								16
Options exercised by executives and directors									62				62
Options exercised by executives and directors (in shares)								14
Net shares repurchased for employee taxes									(215)				(215)
Net shares repurchased for employee taxes, (in shares)								(3)
Treasury stock from cashless options									750			$ (750)
Treasury stock from cashless options, (in shares)								9
Other comprehensive income (loss)										(84)			(84)
Cash dividends declared to stockholders											(5,723)		(5,723)
Balance at Mar. 31, 2018								$ 12	6,369	(244)	108,243	(750)	113,630
Balance (in shares) at Mar. 31, 2018								12,139
Balance at Dec. 31, 2017	$ 12	$ 4,967	$ (160)	$ 103,762	$ 108,581			$ 12	4,967	(160)	101,744		106,563
Balance (in shares) at Dec. 31, 2017	12,103							12,103
Net income													40,136
Net shares repurchased for employee taxes, (in shares)								(3)
Other comprehensive income (loss)													(106)
Balance at Sep. 30, 2018								$ 12	8,040	(266)	124,601	(20,746)	111,641
Balance (in shares) at Sep. 30, 2018								12,145
Balance at Mar. 31, 2018								$ 12	6,369	(244)	108,243	(750)	113,630
Balance (in shares) at Mar. 31, 2018								12,139
Net income											14,133		14,133
Share-based compensation									830				830
Options exercised by executives and directors (in shares)								2
Other comprehensive income (loss)										25			25
Treasury stock from stock repurchases												(19,996)	(19,996)
Cash dividends declared to stockholders											(5,759)		(5,759)
Balance at Jun. 30, 2018								$ 12	7,199	(219)	116,617	(20,746)	102,863
Balance (in shares) at Jun. 30, 2018								12,141
Net income											13,781		13,781
Share-based compensation									717				717
Options exercised by executives and directors									158				158
Options exercised by executives and directors (in shares)								4
Net shares repurchased for employee taxes									(34)				(34)
Other comprehensive income (loss)										(47)			(47)
Cash dividends declared to stockholders											(5,797)		(5,797)
Balance at Sep. 30, 2018								$ 12	8,040	(266)	124,601	(20,746)	111,641
Balance (in shares) at Sep. 30, 2018								12,145
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 (loss)										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)								(1)
Other comprehensive income (loss)													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 (loss)										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 (loss)										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