Annual report pursuant to Section 13 and 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 12 Months Ended
Jun. 30, 2017
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Sep. 22, 2017
Jun. 09, 2017
Temporary Equity [Line Items]                            
Redeemable convertible preferred stock, liquidation preference   $ 1,000               $ 1,000        
Proceeds from issuance of redeemable convertible preferred stock                   $ 480,000,000 $ 0 $ 0    
Contract termination fee and related legal and professional fees   $ 0 $ (423,000) $ 23,467,000 $ 0 $ 0 $ 0 $ 0 $ 0 $ 23,044,000 $ 0 $ 0    
Series A convertible preferred stock                            
Temporary Equity [Line Items]                            
Agreement to sell shares (in shares) 480,000     480,000                    
Redeemable convertible preferred stock, liquidation preference $ 1,000 $ 1,000   $ 1,000           $ 1,000        
Agreement to sell shares $ 480,000,000.0     $ 480,000,000.0                    
Payments of Stock Issuance Costs                   $ 29,318,000        
Proceeds from issuance of redeemable convertible preferred stock                   $ 450,700,000        
Shares conversion per share 95.2381     95.2381                    
Conversion price (in dollars per share) $ 10.50     $ 10.50                    
Quarterly dividend rate, percentage 6.00%                          
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
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