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Marketable Securities - Available-for-sale Securities by Major Security Type (Details) - USD ($)
$ in Thousands
Mar. 31, 2022
Dec. 31, 2021
Marketable Securities [Line Items]    
Amortized cost $ 965 $ 3,007
Gross unrealized holding gains 1 8
Gross unrealized holding losses (26) (5)
Estimated fair value 940 3,010
Corporate bonds and notes [Member]    
Marketable Securities [Line Items]    
Amortized cost 511 1,434
Gross unrealized holding gains 1 8
Gross unrealized holding losses (13) (2)
Estimated fair value 499 1,440
Municipal bonds [Member]    
Marketable Securities [Line Items]    
Amortized cost 454 1,573
Gross unrealized holding gains 0 0
Gross unrealized holding losses (13) (3)
Estimated fair value $ 441 $ 1,570