Quarterly report pursuant to Section 13 or 15(d)

Redeemable Convertible Preferred Stock - Narrative (Details)

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Redeemable Convertible Preferred Stock - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Jun. 30, 2017
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Sep. 22, 2017
Jun. 09, 2017
Temporary Equity [Line Items]              
Proceeds from issuance of redeemable convertible preferred stock       $ 480,000,000 $ 0    
Contract termination fee and related legal and professional fees   $ 423,000 $ 0 (23,044,000) $ 0    
Series A convertible preferred stock              
Temporary Equity [Line Items]              
Agreement to sell shares (in shares) 480,000           480,000
Share price (in dollars per share) $ 1,000            
Agreement to sell shares $ 480,000,000.0            
Shares conversion per share 95.2381            
Conversion price (in dollars per share) $ 10.50           $ 10.50
Quarterly dividend rate, percentage 6.00%            
Right to redeem, period 3 years            
Holder right to redeem, period 5 years            
Redemption percentage 100.00%            
Series A convertible preferred stock | Initial closing              
Temporary Equity [Line Items]              
Agreement to sell shares (in shares)             172,500
Agreement to sell shares             $ 172,500,000
Proceeds from issuance of redeemable convertible preferred stock   15,300,000   292,200,000      
Series A convertible preferred stock | Second closing              
Temporary Equity [Line Items]              
Agreement to sell shares (in shares)           307,500  
Agreement to sell shares           $ 307,500,000  
Proceeds from issuance of redeemable convertible preferred stock   $ 29,300,000   $ 450,700,000