CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Convertible Preferred Stock	Redeemable Common Stock
Beginning balance (in shares) at Dec. 31, 2019							33,443,969	5,901,863
Beginning balance at Dec. 31, 2019							$ 61,216	$ 19,025
Ending balance (in shares) at Mar. 31, 2020							33,443,969	5,901,863
Ending balance at Mar. 31, 2020							$ 61,216	$ 19,025
Beginning balance (in shares) at Dec. 31, 2019		5,746,216
Beginning balance at Dec. 31, 2019	$ 13,295	$ 1	$ (11,431)	$ 8,641	$ 6	$ 16,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	503			503
Exercise of stock options (in shares)		58,452
Exercise of stock options	74			74
Other comprehensive income (loss)	20				20
Net income	904					904
Ending balance (in shares) at Mar. 31, 2020		5,804,668
Ending balance at Mar. 31, 2020	14,796	$ 1	(11,431)	9,218	26	16,982
Beginning balance (in shares) at Dec. 31, 2019							33,443,969	5,901,863
Beginning balance at Dec. 31, 2019							$ 61,216	$ 19,025
Ending balance (in shares) at Sep. 30, 2020							33,443,969	0
Ending balance at Sep. 30, 2020							$ 61,216	$ 0
Beginning balance (in shares) at Dec. 31, 2019		5,746,216
Beginning balance at Dec. 31, 2019	13,295	$ 1	(11,431)	8,641	6	16,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	7,788
Ending balance (in shares) at Sep. 30, 2020		11,727,535
Ending balance at Sep. 30, 2020	46,924	$ 2	(11,432)	34,486	2	23,866
Beginning balance (in shares) at Mar. 31, 2020							33,443,969	5,901,863
Beginning balance at Mar. 31, 2020							$ 61,216	$ 19,025
Ending balance (in shares) at Jun. 30, 2020							33,443,969	5,901,863
Ending balance at Jun. 30, 2020							$ 61,216	$ 19,025
Beginning balance (in shares) at Mar. 31, 2020		5,804,668
Beginning balance at Mar. 31, 2020	14,796	$ 1	(11,431)	9,218	26	16,982
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	505			505
Other comprehensive income (loss)	(17)				(17)
Net income	653					653
Ending balance (in shares) at Jun. 30, 2020		5,804,668
Ending balance at Jun. 30, 2020	15,937	$ 1	(11,431)	9,723	9	17,635
Increase (Decrease) in Temporary Equity [Roll Forward]
Reclassification of redeemable common stock (in shares)								(5,901,863)
Reclassification of redeemable common stock								$ (19,025)
Ending balance (in shares) at Sep. 30, 2020							33,443,969	0
Ending balance at Sep. 30, 2020							$ 61,216	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,451			1,451
Exercise of stock options (in shares)		21,584
Exercise of stock options	20			20
Repurchase of treasury stock, at cost (in shares)		(580)
Repurchase of treasury stock, at cost	(1)		(1)
Repayment of stockholders' notes receivable and accrued interest	4,268			4,268
Issuance of common stock related to RSU vesting (in shares)		5,901,863
Reclassifications of Temporary to Permanent Equity	19,025	$ 1		19,024
Other comprehensive income (loss)	(7)				(7)
Net income	6,231					6,231
Ending balance (in shares) at Sep. 30, 2020		11,727,535
Ending balance at Sep. 30, 2020	46,924	$ 2	(11,432)	34,486	2	23,866
Beginning balance (in shares) at Dec. 31, 2020							0	0
Beginning balance at Dec. 31, 2020							$ 0	$ 0
Ending balance (in shares) at Mar. 31, 2021							0	0
Ending balance at Mar. 31, 2021							$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2020		48,988,142
Beginning balance at Dec. 31, 2020	175,427	$ 6	(11,434)	144,163	1	42,691
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,318			3,318
Exercise of stock options (in shares)		278,412
Exercise of stock options	451			451
Repurchase of treasury stock, at cost (in shares)		(693)
Repurchase of treasury stock, at cost	(27)		(27)
Other comprehensive income (loss)	(1)				(1)
Net income	4,918					4,918
Ending balance (in shares) at Mar. 31, 2021		49,265,861
Ending balance at Mar. 31, 2021	184,086	$ 6	(11,461)	147,932	0	47,609
Beginning balance (in shares) at Dec. 31, 2020							0	0
Beginning balance at Dec. 31, 2020							$ 0	$ 0
Ending balance (in shares) at Sep. 30, 2021							0	0
Ending balance at Sep. 30, 2021							$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2020		48,988,142
Beginning balance at Dec. 31, 2020	$ 175,427	$ 6	(11,434)	144,163	1	42,691
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,694,511
Net income	$ 28,365
Ending balance (in shares) at Sep. 30, 2021		50,880,338
Ending balance at Sep. 30, 2021	220,837	$ 6	(11,486)	161,261	0	71,056
Beginning balance (in shares) at Mar. 31, 2021							0	0
Beginning balance at Mar. 31, 2021							$ 0	$ 0
Ending balance (in shares) at Jun. 30, 2021							0	0
Ending balance at Jun. 30, 2021							$ 0	$ 0
Beginning balance (in shares) at Mar. 31, 2021		49,265,861
Beginning balance at Mar. 31, 2021	184,086	$ 6	(11,461)	147,932	0	47,609
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,837			3,837
Exercise of stock options (in shares)		800,426
Exercise of stock options	1,627			1,627
Repurchase of treasury stock, at cost (in shares)		(449)
Repurchase of treasury stock, at cost	(25)		(25)
Issuance of common stock related to employee stock purchase plan (in shares)		155,015
Issuance of common stock related to employee stock purchase plan	2,635			2,635
Issuance of common stock related to RSU vesting (in shares)		21,973
Net income	9,921					9,921
Ending balance (in shares) at Jun. 30, 2021		50,242,826
Ending balance at Jun. 30, 2021	202,081	$ 6	(11,486)	156,031	0	57,530
Ending balance (in shares) at Sep. 30, 2021							0	0
Ending balance at Sep. 30, 2021							$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,981			3,981
Exercise of stock options (in shares)		615,673
Exercise of stock options	1,249			1,249
Issuance of common stock related to RSU vesting (in shares)		21,839
Net income	13,526					13,526
Ending balance (in shares) at Sep. 30, 2021		50,880,338
Ending balance at Sep. 30, 2021	$ 220,837	$ 6	$ (11,486)	$ 161,261	$ 0	$ 71,056