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 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2017
Jun. 09, 2017
Temporary Equity [Line Items]              
Proceeds from issuance of redeemable convertible preferred stock       $ 172,500,000 $ 0    
Contract termination fee $ (23,500,000) $ (23,467,000) $ 0 $ (23,467,000) $ 0    
Series A convertible preferred stock              
Temporary Equity [Line Items]              
Agreement to sell shares (in shares) 480,000 480,000   480,000     480,000
Share price (in dollars per share) $ 1,000 $ 1,000   $ 1,000      
Agreement to sell shares $ 480,000,000.0 $ 480,000,000.0   $ 480,000,000.0      
Preferred stock issuance costs   13,900,000   13,935,000      
Proceeds from issuance of redeemable convertible preferred stock   $ 158,600,000   $ 158,600,000      
Shares conversion per share 95.2381 95.2381   95.2381      
Conversion price (usd per share) $ 10.50 $ 10.50   $ 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) 172,500 172,500   172,500      
Agreement to sell shares $ 172,500,000 $ 172,500,000   $ 172,500,000      
Series A convertible preferred stock | Closing upon certain regulatory approvals | Forecast              
Temporary Equity [Line Items]              
Agreement to sell shares (in shares)           307,500  
Agreement to sell shares           $ 307,500,000