Redeemable Convertible Preferred Stock - Tranche Rights Issued with Series A Preferred Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair value of Tranche Rights
Change in fair value of preferred stock tranche liability		$ 9,750	$ 1,949
Accrued dividends on temporary equity		1,245
Tranche Right I
Fair value of Tranche Rights
Fair value of Tranche Right Asset			1,500
Proceeds from issuance of stock, net of issuance costs			18,500
Tranche Right II
Fair value of Tranche Rights
Fair value of Tranche Right Liability			$ 4,100
Other financing expense | Tranche Right I
Fair value of Tranche Rights
Change in fair value of preferred stock tranche liability		300
Other financing expense | Tranche Right II
Fair value of Tranche Rights
Change in fair value of preferred stock tranche liability	$ 9,800	2,200
Series B preferred stock
Fair value of Tranche Rights
Proceeds from issuance of stock, net of issuance costs		$ 89,800
Redeemable Convertible Preferred Stock Series A
Temporary Equity [Line Items]
Price per share		$ 1.00	$ 1.00
Fair value of Tranche Rights
Proceeds from issuance of stock, net of issuance costs	$ 32
Redeemable Convertible Preferred Stock Series A | Tranche Right I
Temporary Equity [Line Items]
Number of additional shares of temporary equity contingently obligated to be purchased by temporary equity holders	18,500,000
Price per share	$ 1.00
Fair value of Tranche Rights
Issuance of stock (in shares)		18,500,000
Redeemable Convertible Preferred Stock Series A | Tranche Right II
Temporary Equity [Line Items]
Number of additional shares of temporary equity contingently obligated to be purchased by temporary equity holders	20,000,000
Fair value of Tranche Rights
Redeemable convertible preferred stock, initial carrying amount	$ 36,100
Accrued dividends on temporary equity	$ 1,200
Redeemable Convertible Preferred Stock Series B
Temporary Equity [Line Items]
Price per share	$ 3.00