Annual report pursuant to Section 13 and 15(d)

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

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Common Stock Options, Restricted Stock and Changes In Capitalization - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended 44 Months Ended
Feb. 17, 2017
Dec. 21, 2016
Mar. 15, 2016
Jun. 12, 2015
Apr. 21, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
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 $ 411,700 $ 479,700 $ 501,800 $ (5,364) $ 1,110,555 $ 981,568        
Vitruvian                        
Class of Stock [Line Items]                        
Total initial 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 | 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 11,500,000 10,925,000 23,852,117 50,255,000 22,425,000        
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)           1,939,053       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