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Marketable Securities
9 Months Ended
Sep. 30, 2021
Investments [Abstract]  
Marketable Securities Marketable Securities
The amortized cost, unrealized gain (loss), and estimated fair value of the Company's investments in securities available for sale consisted of the following:
September 30, 2021
Amortized CostUnrealized GainUnrealized LossEstimated Fair Value
Marketable securities
U.S. government securities$374,849 $$(257)$374,593 
Commercial paper16,880— 16,880
Asset-backed securities2,017— 2,017
Corporate debt securities15,4683(7)15,464
Total marketable securities$409,214 $$(264)$408,954 
December 31, 2020
Amortized CostUnrealized GainUnrealized LossEstimated Fair Value
Marketable securities
U.S. government securities$125,823 $47 $(6)$125,864 
Commercial paper4,991— 4,991
Asset-backed securities4,29421— 4,315
Corporate debt securities14,68352(2)14,733
Total marketable securities$149,791 $120 $(8)$149,903 
The Company had sixteen and six separate marketable securities in unrealized loss positions as of September 30, 2021 and December 31, 2020, respectively. The Company did not identify any marketable securities that were other-than-temporarily impaired as of September 30, 2021 and December 31, 2020.
The following table summarizes the stated maturities of the Company’s marketable securities:
September 30, 2021December 31, 2020
Amortized CostEstimated Fair ValueAmortized CostEstimated Fair Value
Due within one year$56,756 $56,756 $149,791 $149,903 
Due after one year through two years352,458352,198
Total$409,214 $408,954 $149,791 $149,903