Quarterly report pursuant to Section 13 or 15(d)

Common Stock and Changes in Capitalization (Narrative) (Details)

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Common Stock and Changes in Capitalization (Narrative) (Details) - USD ($)
$ in Thousands
 9 Months Ended
Feb. 17, 2017
Mar. 15, 2016
Sep. 30, 2017
Sep. 30, 2016
Class of Stock [Line Items]        
Proceeds from issuance of common stock, after underwriting discounts and commissions and offering expenses   $ 411,700 $ (5,364) $ 411,711
Vitruvian acquisition        
Class of Stock [Line Items]        
Total initial purchase price $ 1,850,000      
Payments to acquire businesses $ 1,354,093      
Equity interest issued or issuable, number of shares (in shares) 23,900,000      
Vitruvian acquisition | Indemnity escrow        
Class of Stock [Line Items]        
Equity interest issued or issuable, number of shares (in shares) 5,200,000      
Common Stock        
Class of Stock [Line Items]        
Issuance of common stock in public offerings (in shares)   16,905,000   16,905,000
Common Stock | Over-allotment option        
Class of Stock [Line Items]        
Issuance of common stock in public offerings (in shares)   2,205,000