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Marketable Securities
 12 Months Ended
Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]  
Marketable Securities [Text Block] Marketable Securities
 
2019
 
2018
 
Cost
 
Unrealized
Gains (Losses)
 
Fair
Value
 
Cost
 
Unrealized
Gains (Losses)
 
Fair
Value
U.S. government securities
$
—

 
$
—

 
$
—

 
$
2

 
$
—

 
$
2

Corporate securities


 


 
—

 
4

 


 
4

Certificates of deposit
19

 


 
19

 
15

 


 
15

Total marketable securities
$
19

 
$
—

 
$
19

 
$
21

 
$
—

 
$
21



U.S. government securities include bonds issued by government-sponsored agencies and Treasury notes. Corporate securities are primarily debt securities. Certificates of deposit maturing in one year or less total $19 at December 31, 2019.