Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	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	138		138
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		132,348
Stock-based compensation	270		270
Net income (loss)	473			473
Ending Balances at Mar. 31, 2018	25,849	$ 2	17,988	7,859
Ending Balances, Shares at Mar. 31, 2018		16,884,519
Beginning Balances at Dec. 31, 2017	24,968	$ 2	17,580	7,386
Beginning Balances, Shares at Dec. 31, 2017		16,752,171
Net income (loss)	1,238
Ending Balances at Sep. 30, 2018	27,585	$ 2	18,959	8,624
Ending Balances, Shares at Sep. 30, 2018		17,074,636
Beginning Balances at Mar. 31, 2018	25,849	$ 2	17,988	7,859
Beginning Balances, Shares at Mar. 31, 2018		16,884,519
Issuance of common stock upon exercise of stock options and vesting of early exercised options	122		122
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		114,658
Stock-based compensation	193		193
Net income (loss)	201			201
Ending Balances at Jun. 30, 2018	26,365	$ 2	18,303	8,060
Ending Balances, Shares at Jun. 30, 2018		16,999,177
Issuance of common stock upon exercise of stock options and vesting of early exercised options	105		105
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		75,459
Stock-based compensation	551		551
Net income (loss)	564			564
Ending Balances at Sep. 30, 2018	27,585	$ 2	18,959	8,624
Ending Balances, Shares at Sep. 30, 2018		17,074,636
Beginning Balances at Dec. 31, 2018	28,631	$ 2	19,358	9,271
Beginning Balances, Shares at Dec. 31, 2018		17,130,507
Issuance of common stock upon exercise of stock options and vesting of early exercised options	64		64
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		46,666
Issuance of common stock upon vesting of RSUs, Shares		14,200
Shares repurchased for tax withholdings on vesting of RSUs	(7)		(7)
Shares repurchased for tax withholdings on vesting of RSUs, Shares		(1,510)
Stock-based compensation	336		336
Net income (loss)	(618)			(618)
Ending Balances at Mar. 31, 2019	28,406	$ 2	19,751	8,653
Ending Balances, Shares at Mar. 31, 2019		17,189,863
Beginning Balances at Dec. 31, 2018	28,631	$ 2	19,358	9,271
Beginning Balances, Shares at Dec. 31, 2018		17,130,507
Net income (loss)	1,174
Ending Balances at Sep. 30, 2019	30,949	$ 2	20,502	10,445
Ending Balances, Shares at Sep. 30, 2019		17,369,590
Beginning Balances at Mar. 31, 2019	28,406	$ 2	19,751	8,653
Beginning Balances, Shares at Mar. 31, 2019		17,189,863
Issuance of common stock upon exercise of stock options and vesting of early exercised options	36		36
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		38,000
Issuance of common stock upon vesting of RSUs, Shares		31,300
Shares repurchased for tax withholdings on vesting of RSUs	(24)		(24)
Shares repurchased for tax withholdings on vesting of RSUs, Shares		(3,553)
Stock-based compensation	348		348
Net income (loss)	335			335
Ending Balances at Jun. 30, 2019	29,101	$ 2	20,111	8,988
Ending Balances, Shares at Jun. 30, 2019		17,255,610
Issuance of common stock upon exercise of stock options and vesting of early exercised options	80		80
Issuance of common stock upon exercise of stock options and vesting of early exercised options, Shares		100,015
Issuance of common stock upon vesting of RSUs, Shares		17,925
Shares repurchased for tax withholdings on vesting of RSUs	(26)		(26)
Shares repurchased for tax withholdings on vesting of RSUs, Shares		(3,960)
Stock-based compensation	337		337
Net income (loss)	1,457			1,457
Ending Balances at Sep. 30, 2019	$ 30,949	$ 2	$ 20,502	$ 10,445
Ending Balances, Shares at Sep. 30, 2019		17,369,590