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Short-term Investments
 9 Months Ended
Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]  
Short-term Investments Short-term Investments
    Short-term investments consisted of available-for-sale and equity securities as follows (in thousands):
Type of securities as of September 30, 2020Amortized
cost		Gross
unrealized
gains		Gross
unrealized
losses		Fair value
Corporate debt securities$42,865 $180 $— $43,045 
U.S. government-related debt securities15,001 51 — 15,052 
Asset-backed securities1,463 14 — 1,477 
Total available-for-sale debt securities$59,329 $245 $— $59,574 
Type of securities as of December 31, 2019Amortized
cost		Gross
unrealized
gains		Gross
unrealized
losses		Fair value
Corporate debt securities$78,243 $89 $(2)$78,330 
U.S. government-related debt securities26,966 37 — 27,003 
Asset-backed securities11,950 21 — 11,971 
Total available-for-sale debt securities$117,159 $147 $(2)$117,304 
Corporate equity securities9,893 625 — 10,518 
Total short-term investment securities$127,052 $772 $(2)$127,822 

    The fair values of available-for-sale debt securities by contractual maturity were as follows (in thousands):
September 30, 2020December 31, 2019
Maturing in one year or less$59,574 $101,751 
Maturing in one to three years— 15,553 
Total available-for-sale debt securities$59,574 $117,304