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 ($)
 3 Months Ended
Feb. 17, 2017
Mar. 31, 2018
Jan. 31, 2018
Class of Stock [Line Items]      
Stock repurchase program, amount authorized to acquire     $ 100,000,000
Amount of shares repurchased   $ 99,997,000  
Vitruvian acquisition      
Class of Stock [Line Items]      
Total initial purchase price $ 1,850,000,000    
Payments to acquire businesses $ 1,354,093,000    
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]      
Shares repurchased (in shares)   9,692,356  
Amount of shares repurchased   $ 97,000