Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning Balances at Dec. 31, 2017	$ 24,968	$ 2	$ 17,580		$ 7,386
Beginning Balances, Shares at Dec. 31, 2017		16,752,171
Issuance of common stock upon exercise of stock options and vesting of early exercised options	423		423
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		368,632
Issuance of common stock upon vesting of restricted stock units, Shares		10,500
Shares repurchased for tax withholdings on vesting of restricted stock units	(9)		(9)
Shares repurchased for tax withholdings on vesting of restricted stock units, Shares		(796)
Stock-based compensation	1,364		1,364
Net income	1,885				1,885
Ending Balances at Dec. 31, 2018	28,631	$ 2	19,358		9,271
Ending Balances, Shares at Dec. 31, 2018		17,130,507
Other comprehensive (income) loss - unrealized gain (loss) on available-for-sale debt securities	(15)			$ (15)
Issuance of common stock upon exercise of stock options and vesting of early exercised options	243		243
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		249,848
Issuance of common stock upon vesting of restricted stock units, Shares		82,600
Shares repurchased for tax withholdings on vesting of restricted stock units	(88)		(88)
Shares repurchased for tax withholdings on vesting of restricted stock units, Shares		(13,383)
Stock-based compensation	1,415		1,415
Net income	2,194				2,194
Ending Balances at Dec. 31, 2019	32,380	$ 2	20,928	(15)	11,465
Ending Balances, Shares at Dec. 31, 2019		17,449,572
Other comprehensive (income) loss - unrealized gain (loss) on available-for-sale debt securities	56			56
Issuance of common stock upon exercise of stock options and vesting of early exercised options	224		224
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		123,817
Issuance of common stock upon vesting of restricted stock units, Shares		141,175
Shares repurchased for tax withholdings on vesting of restricted stock units	(115)		(115)
Shares repurchased for tax withholdings on vesting of restricted stock units, Shares		(24,502)
Stock-based compensation	1,486		1,486
Net income	3,342				3,342
Ending Balances at Dec. 31, 2020	$ 37,373	$ 2	$ 22,523	$ 41	$ 14,807
Ending Balances, Shares at Dec. 31, 2020		17,690,062