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Business and Summary of Significant Accounting Policies - Initial Public Offering (Details) - USD ($)
$ / shares in Units, $ in Millions
Jul. 30, 2018
Jun. 30, 2019
Dec. 31, 2018
Class of Stock [Line Items]      
Common stock, authorized (in shares) 500,000,000 500,000,000 500,000,000
Preferred stock, authorized (in shares) 10,000,000    
IPO      
Class of Stock [Line Items]      
Stock sold, price per share (in usd per share) $ 23.00    
Net proceeds from sale of stock $ 264.6    
Common Stock | IPO      
Class of Stock [Line Items]      
Stock sold (in shares) 12,535,000    
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares) 55,385,854    
Common Stock | Over-allotment option      
Class of Stock [Line Items]      
Stock sold (in shares) 1,635,000    
Redeemable convertible Series A preferred stock | IPO      
Class of Stock [Line Items]      
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares) 15,847,500    
Redeemable convertible Series B preferred stock | IPO      
Class of Stock [Line Items]      
Issuance of common stock upon conversion of redeemable convertible preferred stock (in shares) 39,538,354