CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Total
Balance at Dec. 31, 2018	$ 191	$ 30,111	$ 286,756	$ (15,876)	$ 301,182
Balance (in shares) at Dec. 31, 2018	17,919,021
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		241		804	1,045
Net exercise of stock options (in shares)	57,670
Stock-based compensation expense		915			915
Net income (loss)			7,015		7,015
Balance at Mar. 31, 2019	$ 191	31,267	293,771	(15,072)	310,157
Balance (in shares) at Mar. 31, 2019	17,976,691
Balance at Dec. 31, 2018	$ 191	30,111	286,756	(15,876)	301,182
Balance (in shares) at Dec. 31, 2018	17,919,021
Increase (Decrease) in Stockholders' Equity
Net income (loss)					25,620
Balance at Sep. 30, 2019	$ 191	33,728	312,376	(13,602)	332,693
Balance (in shares) at Sep. 30, 2019	18,082,135
Balance at Mar. 31, 2019	$ 191	31,267	293,771	(15,072)	310,157
Balance (in shares) at Mar. 31, 2019	17,976,691
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		141		545	686
Net exercise of stock options (in shares)	39,043
Stock-based compensation expense		1,003			1,003
Net income (loss)			9,279		9,279
Balance at Jun. 30, 2019	$ 191	32,411	303,050	(14,527)	321,125
Balance (in shares) at Jun. 30, 2019	18,015,734
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		290		925	1,215
Net exercise of stock options (in shares)	66,401
Stock-based compensation expense		1,027			1,027
Net income (loss)			9,326		9,326
Balance at Sep. 30, 2019	$ 191	33,728	312,376	(13,602)	332,693
Balance (in shares) at Sep. 30, 2019	18,082,135
Balance at Dec. 31, 2019	$ 191	35,215	318,572	(12,777)	$ 341,201
Balance (in shares) at Dec. 31, 2019	18,141,383				18,141,383
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		(428)		428
Net exercise of stock options (in shares)	30,545
Stock-based compensation expense		873			$ 873
Net income (loss)			2,020		2,020
Balance at Mar. 31, 2020	$ 191	35,660	320,592	(12,349)	344,094
Balance (in shares) at Mar. 31, 2020	18,171,928
Balance at Dec. 31, 2019	$ 191	35,215	318,572	(12,777)	$ 341,201
Balance (in shares) at Dec. 31, 2019	18,141,383				18,141,383
Increase (Decrease) in Stockholders' Equity
Net income (loss)					$ 8,418
Balance at Sep. 30, 2020	$ 191	37,466	326,990	(11,117)	$ 353,530
Balance (in shares) at Sep. 30, 2020	18,260,072				18,260,072
Balance at Mar. 31, 2020	$ 191	35,660	320,592	(12,349)	$ 344,094
Balance (in shares) at Mar. 31, 2020	18,171,928
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		(552)		246	(306)
Net exercise of stock options (in shares)	17,634
Stock-based compensation expense		981			981
Net income (loss)			(4,347)		(4,347)
Balance at Jun. 30, 2020	$ 191	36,089	316,245	(12,103)	340,422
Balance (in shares) at Jun. 30, 2020	18,189,562
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		402		986	1,388
Net exercise of stock options (in shares)	70,510
Stock-based compensation expense		897			897
Capital contribution		78			78
Net income (loss)			10,745		10,745
Balance at Sep. 30, 2020	$ 191	$ 37,466	$ 326,990	$ (11,117)	$ 353,530
Balance (in shares) at Sep. 30, 2020	18,260,072				18,260,072