Nature of Business and Liquidity - Liquidity (Additional Information) (Details) $ / shares in Units, $ in Millions	1 Months Ended
	Jul. 31, 2018 USD ($) vote $ / shares shares	Dec. 31, 2018 $ / shares shares	Dec. 31, 2017 $ / shares shares
Subsidiary, Sale of Stock [Line Items]
Common stock, authorized (in shares)		0	113,333,333
Common stock, par value (in dollars per share) | $ / shares		$ 0	$ 0.0001
Condition for mandatory conversion to Class A	(5.00%)
Convertible redeemable preferred stock, shares authorized (in shares)		80,461,552	80,461,552
IPO
Subsidiary, Sale of Stock [Line Items]
Shares sold in offering (in shares)	20,700,000
Offering price per share (in dollars per share) | $ / shares	$ 15.00
Net proceeds from stock offering | $	$ 282.3
Class A common stock
Subsidiary, Sale of Stock [Line Items]
Common stock, authorized (in shares)		400,000,000	0
Stockholders' vote for each share of common stock | vote	1
Class B common stock
Subsidiary, Sale of Stock [Line Items]
Common stock, authorized (in shares)		400,000,000	0
Stockholders' vote for each share of common stock | vote	10