Annual report pursuant to Section 13 and 15(d)

Common Stock Options, Restricted Stock and Changes In Capitalization (Details)

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Common Stock Options, Restricted Stock and Changes In Capitalization (Details) - USD ($)
 12 Months Ended 44 Months Ended
Feb. 17, 2017
Dec. 21, 2016
Mar. 15, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2016
May 31, 2018
Jan. 31, 2018
Apr. 19, 2013
Apr. 20, 2006
Apr. 19, 2006
Class of Stock [Line Items]                        
Granted for purchase of previous plan's common stock (shares)       0 0 0            
Proceeds from issuance of common stock, net of offering costs and exercise of stock options   $ 698,800,000 $ 411,700,000   $ (5,364,000) $ 1,110,555,000            
Stock repurchase program, authorized amount               $ 200,000,000 $ 100,000,000      
Stock repurchase program, additional authorized amount               $ 100,000,000        
Stock repurchased and retired during period (shares)       20,700,000                
Stock repurchased and retired during period, net of tax       $ 200,000,000                
Shares repurchased for tax withholding requirement (in shares)       29,000                
Tax withholding requirement       $ 300,000                
Vitruvian                        
Class of Stock [Line Items]                        
Total initial 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 | 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 offering (shares)   33,350,000 16,905,000     50,255,000            
Stock repurchased and retired during period (shares)       20,746,536                
2005 Stock Incentive Plan | Common Stock                        
Class of Stock [Line Items]                        
Available for grant (shares)                     3,000,000 1,904,606
Granted for purchase of previous plan's common stock (shares)       997,269                
1999 Stock Option Plan | Common Stock                        
Class of Stock [Line Items]                        
Granted to employees under previous plan (shares)                     627,337  
2013 Restated Stock Incentive Plan | Common Stock                        
Class of Stock [Line Items]                        
Available for grant (shares)       3,518,964           7,500,000 3,000,000  
Granted for purchase of previous plan's common stock (shares)             627,337          
Over-allotment option | Common Stock                        
Class of Stock [Line Items]                        
Issuance of common stock in public offering (shares)   4,350,000 2,205,000                  
Restricted stock | 2005 Stock Incentive Plan                        
Class of Stock [Line Items]                        
Granted for purchase of previous plan's common stock (shares)       1,143,217