Stockholders' Deficit and Redeemable Convertible Preferred Stock - Convertible Preferred Stock (Details) $ / shares in Units, $ in Thousands			9 Months Ended	12 Months Ended
	Oct. 04, 2016 shares	Oct. 03, 2016 payment $ / shares	Oct. 03, 2016 USD ($) Vote $ / shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Accretion of issuance costs | $				$ 11	$ 50	$ 50
Number of votes per share | Vote			1
Series A and Series A-1 redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Stated value (in dollars per share) | $ / shares					$ 0.0001
Number of annual installment payments for preferred stock redemption amounts | payment		3
Period of written notice			180 days
Series A redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Annual dividend rate (as a percent)					6.00%
Stated value (in dollars per share) | $ / shares		$ 0.68	$ 0.68
Aggregate amount of cumulative unpaid dividends | $			$ 1,223		$ 1,042
Series A-1 redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Annual dividend rate (as a percent)					6.00%
Stated value (in dollars per share) | $ / shares		0.80	$ 0.80
Aggregate amount of cumulative unpaid dividends | $			$ 661		$ 547
Series B redeemable convertible preferred stock
Redeemable Convertible Preferred Stock
Annual dividend rate (as a percent)					6.00%
Stated value (in dollars per share) | $ / shares		$ 1.52	$ 1.52		$ 0.0001
Aggregate amount of cumulative unpaid dividends | $			$ 944		$ 712
Period of written notice			180 days
Common Stock
Redeemable Convertible Preferred Stock
Conversion of redeemable convertible preferred stock upon initial public offering (in shares) | shares	5,089,436			5,089,436