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Short-term Investments
 6 Months Ended
Jun. 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 June 30, 2020Amortized
cost		Gross
unrealized
gains		Gross
unrealized
losses		Fair value
Corporate debt securities$50,859  $291  $—  $51,150  
U.S. government-related debt securities20,009  118  —  20,127  
Asset-backed securities8,960  29  —  8,989  
Total available-for-sale debt securities$79,828  $438  $—  $80,266  
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):
June 30, 2020December 31, 2019
Maturing in one year or less$80,266  $101,751  
Maturing in one to three years—  15,553  
Total available-for-sale debt securities$80,266  $117,304