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Marketable Securities and Fair Value Disclosures - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Details)
$ in Thousands
Dec. 31, 2017
USD ($)
Investments Debt And Equity Securities [Abstract]  
Due in one year or less, Amortized Cost $ 3,052
Amortized Cost 3,052
Due in one year or less, Fair Value 3,050
Fair Value $ 3,050