Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In- Capital	Treasury Stock	Accumulated Deficit
Balance at Dec. 31, 2014	$ (121,844)	$ 0	$ 26	$ 7,168	$ (42)	$ (128,996)
Balance (in shares) at Dec. 31, 2014		0	2,614
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from initial public offering, net of issuance costs	92,953		$ 75	92,878
Issuance of common stock from initial public offering, net of issuance costs (in shares)			7,525
Conversion of redeemable convertible preferred stock to common stock	202,456		$ 350	202,106
Conversion of redeemable convertible preferred stock to common stock (in shares)			35,018
Common stock issued in connection with equity based plans	344		$ 3	341
Common stock issued in connection with equity based plans (in shares)			277
Vesting of common stock subject to repurchase	453		$ 2	451
Vesting of common stock subject to repurchase (in shares)			126
Stock-based compensation expense	3,347			3,347
Tax benefit from stock-based awards, net	700			700
Modification of employee stock-based award and repurchase of common stock	(46)		$ (1)	(45)
Modification of employee stock-based award and repurchase of common stock (in shares)			(75)
Dividends paid to common stockholders	(1,013)			(673)		(340)
Dividends paid to employees with unvested common stock	(57)			(38)		(19)
Dividends paid to redeemable convertible preferred stockholders	(18,930)			(8,454)		(10,476)
Net income	11,768					11,768
Balance at Dec. 31, 2015	170,131	$ 0	$ 455	297,781	(42)	(128,063)
Balance (in shares) at Dec. 31, 2015		0	45,485
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued in connection with equity based plans	1,661		$ 5	1,656
Common stock issued in connection with equity based plans (in shares)			593
Vesting of common stock subject to repurchase	254		$ 1	253
Vesting of common stock subject to repurchase (in shares)			64
Stock-based compensation expense	4,001			4,001
Tax benefit from stock-based awards, net	5,048			5,048
Retirement of treasury stock	0			(42)	42
Net income	10,154					10,154
Balance at Dec. 31, 2016	191,249	$ 0	$ 461	308,697	0	(117,909)
Balance (in shares) at Dec. 31, 2016		0	46,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of accounting standard on employee share based payments	12			31		(19)
Common stock issued in connection with equity based plans	3,450		$ 11	3,439
Common stock issued in connection with equity based plans (in shares)			1,045
Vesting of common stock subject to repurchase	77		$ 0	77
Vesting of common stock subject to repurchase (in shares)			15
Stock-based compensation expense	7,413			7,413
Stock options assumed from acquisition	1,375			1,375
Net income	29,251					29,251
Balance at Dec. 31, 2017	$ 232,827	$ 0	$ 472	$ 321,032	$ 0	$ (88,677)
Balance (in shares) at Dec. 31, 2017		0	47,202