CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Temporary Equity
Balance at beginning of period	$ 28,973	$ 19,007	$ 15,123
Accretion (decretion) of redeemable convertible preferred stock	(2,439)	9,966	3,884
Conversion of redeemable convertible preferred stock upon initial public offering	(26,534)
Balance at end of period		28,973	19,007
Series A redeemable convertible preferred stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period	$ 4,019	$ 3,781	$ 3,556
Balance at beginning of period (in shares)	4,411,766	4,411,766	4,411,766
Accretion (decretion) of redeemable convertible preferred stock	$ 188	$ 238	$ 225
Conversion of redeemable convertible preferred stock upon initial public offering	$ (4,207)
Conversion of redeemable convertible preferred stock upon initial public offering (in shares)	(4,411,766)
Balance at end of period		$ 4,019	$ 3,781
Balance at end of period (in shares)		4,411,766	4,411,766
Series A-1 redeemable convertible preferred stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period	$ 2,534	$ 2,384	$ 2,242
Balance at beginning of period (in shares)	2,500,000	2,500,000	2,500,000
Accretion (decretion) of redeemable convertible preferred stock	$ 118	$ 150	$ 142
Conversion of redeemable convertible preferred stock upon initial public offering	$ (2,652)
Conversion of redeemable convertible preferred stock upon initial public offering (in shares)	(2,500,000)
Balance at end of period		$ 2,534	$ 2,384
Balance at end of period (in shares)		2,500,000	2,500,000
Series B redeemable convertible preferred stock
Increase (Decrease) in Temporary Equity
Balance at beginning of period	$ 22,420	$ 12,842	$ 9,325
Balance at beginning of period (in shares)	2,961,745	2,961,745	2,961,745
Accretion (decretion) of redeemable convertible preferred stock	$ (2,745)	$ 9,578	$ 3,517
Conversion of redeemable convertible preferred stock upon initial public offering	$ (19,675)
Conversion of redeemable convertible preferred stock upon initial public offering (in shares)	(2,961,745)
Balance at end of period		$ 22,420	$ 12,842
Balance at end of period (in shares)	0	2,961,745	2,961,745