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Common Stock and Changes in Capitalization (Details) - USD ($) $ in Thousands |  | 9 Months Ended
--- | --- | ---
Mar. 15, 2016 | Sep. 30, 2016 | Sep. 30, 2015
Class of Stock [Line Items] |  |  |
Proceeds from issuance of common stock, net of offering costs |  | $ 411,711 | $ 981,568
Common Stock | Public Offering |  |  |
Class of Stock [Line Items] |  |  |
Stock issued in underwritten public offering (in shares) | 16,905,000 |  |
Proceeds from issuance of common stock, net of offering costs | $ 411,700 |  |
Common Stock | Over-Allotment Option |  |  |
Class of Stock [Line Items] |  |  |
Stock issued in underwritten public offering (in shares) | 2,205,000 |  |

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