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Marketable Securities (Notes)
 6 Months Ended
Jun. 30, 2017
Marketable Securities [Abstract]  
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
Marketable Securities
Marketable securities as of June 30, 2017 and December 31, 2016 consisted of the following:
June 30, 2017
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Fair
Value
Money market mutual funds
$
8,031

 
$
—

 
$
—

 
$
8,031

United States treasuries
4,014

 
—

 
(3
)
 
4,011

Certificates of deposit
1,729

 
—

 
—

 
1,729

Total marketable securities designated as available-for-sale
$
13,774

 
$
—

 
$
(3
)
 
$
13,771

 
December 31, 2016
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Fair
Value
Money market mutual funds
$
21,848

 
$
—

 
$
—

 
$
21,848

Certificates of deposit
3,864

 
—

 
—

 
3,864

Total marketable securities designated as available-for-sale
$
25,712

 
$
—

 
$
—

 
$
25,712



The amortized costs and fair value of marketable securities as of June 30, 2017 and December 31, 2016 are shown below by effective maturity. Effective maturities may differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties.
June 30, 2017
Amortized
Cost
 
Fair
Value
Due in less than one year
$
5,743

 
$
5,740

December 31, 2016
Amortized
Cost
 
Fair
Value
Due in less than one year
$
3,864

 
$
3,864


Interest income from marketable securities was $30 and $20 during the three months ended June 30, 2017 and 2016,