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Common Stock and Changes in Capitalization (Narrative) (Details) - USD ($) $ in Thousands |  |  | 3 Months Ended
--- | --- | --- | ---
Feb. 17, 2017 | Mar. 15, 2016 | Mar. 31, 2017 | Mar. 31, 2016
Class of Stock [Line Items] |  |  |  |
Proceeds from issuance of common stock, net of offering costs |  | $ 411,900 | $ (5,321) | $ 411,918
Vitruvian acquisition |  |  |  |
Class of Stock [Line Items] |  |  |  |
Total consideration | $ 1,850,000 |  |  |
Payments to acquire businesses | $ 1,354,093 |  |  |
Equity interest issued or issuable, number of shares | 23,900,000 |  |  |
Indemnity escrow | Vitruvian acquisition |  |  |  |
Class of Stock [Line Items] |  |  |  |
Equity interest issued or issuable, number of shares | 5,200,000 |  |  |
Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Issuance of Common Stock in public offerings, net of related expenses (in shares) |  | 16,905,000 |  | 16,905,000
Over-allotment option | Common Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Issuance of Common Stock in public offerings, net of related expenses (in shares) |  | 2,205,000 |  |

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