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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Accounting Policies [Abstract]      
Restricted Cash $ 48,579 $ 7,503 $ 25,336
Payment for Debt Extinguishment or Debt Prepayment Cost $ 0 $ 1,453