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Investments and Fair Value Measurements - Recurring Basis (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Assets, Fair Value Disclosure [Abstract]    
Investments, amortized cost $ 13,085 $ 22,846
Recurring    
Assets, Fair Value Disclosure [Abstract]    
Total 13,085 22,846
Recurring | Certificates of Deposit [Member]    
Assets, Fair Value Disclosure [Abstract]    
Cash and cash equivalents, fair value disclosure 4,496 4,481
Recurring | Corporate Bonds [Member]    
Assets, Fair Value Disclosure [Abstract]    
Investments, amortized cost 8,589 18,365
Recurring | Significant Other Observable Inputs (Level 2)    
Assets, Fair Value Disclosure [Abstract]    
Total 13,085 22,846
Recurring | Significant Other Observable Inputs (Level 2) | Certificates of Deposit [Member]    
Assets, Fair Value Disclosure [Abstract]    
Cash and cash equivalents, fair value disclosure 4,496 4,481
Recurring | Significant Other Observable Inputs (Level 2) | Corporate Bonds [Member]    
Assets, Fair Value Disclosure [Abstract]    
Investments, amortized cost $ 8,589 $ 18,365