Significant Accounting Policies - Narrative (Details)			12 Months Ended
	Dec. 07, 2017 USD ($) $ / shares shares	Nov. 28, 2017 shares	Dec. 31, 2019 USD ($) Segment contract shares	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) shares
Significant Accounting Policies [Line Items]
Common stock, shares authorized (in shares) | shares	400,000,000		400,000,000		400,000,000
Convertible preferred stock, shares authorized (in shares) | shares	40,000,000		40,000,000		40,000,000
Off-balance sheet concentrations of credit risk | $			$ 0		$ 0
Number of operating segments | Segment			1
Number of financing leases | contract			0
Right of use asset | $			$ 33,923,000
Lease liabilities | $			$ 72,530,000
IPO
Significant Accounting Policies [Line Items]
Shares sold during initial public offering (shares) | shares	15,972,221
Share price (usd per share) | $ / shares	$ 18.00
Proceeds from issuance of common stock, net of underwriting discounts and commissions and offering expenses | $	$ 264,300,000
Convertible preferred stock converted into shares of common stock (in shares) | shares	60,365,020
Amount reclassified to common stock and additional paid-in capital | $	$ 378,600,000
Over-Allotment Option
Significant Accounting Policies [Line Items]
Shares sold during initial public offering (shares) | shares	2,083,333
Common Stock
Significant Accounting Policies [Line Items]
Reverse stock split (in shares) | shares		4
Convertible Preferred Stock
Significant Accounting Policies [Line Items]
Reverse stock split (in shares) | shares		4
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Right of use asset | $				$ 46,100,000
Lease liabilities | $				$ 71,300,000