Redeemable Convertible Preferred Stock - Preferred Stock (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) vote director $ / shares shares	Mar. 31, 2017 $ / shares shares	Feb. 28, 2017 $ / shares shares	Dec. 31, 2016 USD ($) shares
Temporary Equity [Line Items]
Shares Authorized (in shares)	0	12,104,749
Redeemable convertible preferred stock issued (in shares)	0	11,871,578
Redeemable convertible preferred stock outstanding (in shares)	0	11,871,578			11,330,704
Carrying Value | $	$ 0	$ 118,548			$ 113,121
Liquidation Value | $	$ 0	$ 119,194
Series 2 common stock, number of directors entitled to elect | director		2
Shareholder approval, minimum shares outstanding (in shares)		277,778
Preferred stock dividends declared (in dollars per share) | $ / shares	$ 0	$ 0
Common stock dividends declared (in dollars per share) | $ / shares	$ 0	$ 0
Minimum public offering for conversion | $		$ 50,000
Minimum public offering per share for conversion (in dollars per share) | $ / shares		$ 30.0996
Series 1 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		245,096
Redeemable convertible preferred stock issued (in shares)		245,096
Redeemable convertible preferred stock outstanding (in shares)		245,096
Carrying Value | $		$ 154
Liquidation Value | $		$ 154
Preferred stock votes per share | vote		0.352941
Dividend rate (in dollars per share) | $ / shares		$ 0.050112
Liquidation preference per share (in dollars per share) | $ / shares		$ 0.6264
Series 2 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		709,617
Redeemable convertible preferred stock issued (in shares)		709,608
Redeemable convertible preferred stock outstanding (in shares)		709,608
Carrying Value | $		$ 1,489
Liquidation Value | $		$ 1,520
Preferred stock votes per share | vote		0.352941
Dividend rate (in dollars per share) | $ / shares		$ 0.171360
Liquidation preference per share (in dollars per share) | $ / shares		$ 2.142
Series 3 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		498,958
Redeemable convertible preferred stock issued (in shares)		498,938
Redeemable convertible preferred stock outstanding (in shares)		498,938
Carrying Value | $		$ 2,862
Liquidation Value | $		$ 2,874
Preferred stock votes per share | vote		0.352941
Dividend rate (in dollars per share) | $ / shares		$ 0.4608
Liquidation preference per share (in dollars per share) | $ / shares		$ 5.76
Series 4 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		2,509,047
Redeemable convertible preferred stock issued (in shares)		2,509,032
Redeemable convertible preferred stock outstanding (in shares)		2,509,032
Carrying Value | $		$ 15,656
Liquidation Value | $		$ 15,807
Preferred stock votes per share | vote		1
Preferred stock, number of directors entitled to elect | director		1
Dividend rate (in dollars per share) | $ / shares		$ 0.504
Liquidation preference per share (in dollars per share) | $ / shares		6.30
Liquidation participation cap per share (in dollars per share) | $ / shares		$ 12.60
Series 5 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		2,086,138
Redeemable convertible preferred stock issued (in shares)		2,009,226
Redeemable convertible preferred stock outstanding (in shares)		2,009,226
Carrying Value | $		$ 18,127
Liquidation Value | $		$ 18,275
Preferred stock votes per share | vote		1
Preferred stock, number of directors entitled to elect | director		1
Dividend rate (in dollars per share) | $ / shares		$ 0.72774
Liquidation preference per share (in dollars per share) | $ / shares		9.0954
Liquidation participation cap per share (in dollars per share) | $ / shares		$ 18.1908
Series 6 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		3,389,227
Redeemable convertible preferred stock issued (in shares)		3,319,274
Redeemable convertible preferred stock outstanding (in shares)		3,319,274
Carrying Value | $		$ 54,508
Liquidation Value | $		$ 54,674
Preferred stock votes per share | vote		1
Preferred stock, number of directors entitled to elect | director		1
Dividend rate (in dollars per share) | $ / shares		$ 1.317744
Liquidation preference per share (in dollars per share) | $ / shares		16.4718
Liquidation participation cap per share (in dollars per share) | $ / shares		$ 32.9436
Conversion price (in dollars per share) | $ / shares			$ 15.5574	$ 15.714
Conversion ratio (in shares)			1.06	1.05
Series 7 Preferred Stock
Temporary Equity [Line Items]
Shares Authorized (in shares)		2,666,666
Redeemable convertible preferred stock issued (in shares)		2,580,404
Redeemable convertible preferred stock outstanding (in shares)		2,580,404
Carrying Value | $		$ 25,752
Liquidation Value | $		$ 25,890
Preferred stock votes per share | vote		1
Preferred stock, number of directors entitled to elect | director		1
Dividend rate (in dollars per share) | $ / shares		$ 0.802656
Liquidation preference per share (in dollars per share) | $ / shares		$ 10.0332