Investment securities (Tables)
 9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]    
Schedule Of Investment Securities Reconciliation
The following tables present amortized cost and fair values of investments as of September 30, 2021, and December 31, 2020, respectively:
September 30, 2021Amortized costAccumulated unrealized gainsAccumulated unrealized lossesFair value
(in thousands)
Investment securities, held-to-maturity
U.S. government and government agencies and authorities$695 $42 $(10)$727 
Investment securities, available-for-sale
U.S. government and government agencies and authorities167,935 37 (647)167,325 
Total investment securities$168,630 $79 $(657)$168,052 
December 31, 2020Amortized costAccumulated unrealized gainsAccumulated unrealized lossesFair value
(in thousands)
Investment securities, held-to-maturity
U.S. government and government agencies and authorities$694 $43 $— $737 
Investment securities, available-for-sale
U.S. government and government agencies and authorities53,953 51 (41)53,963 
Total investment securities$54,647 $94 $(41)$54,700 
The following tables present cost or amortized cost and fair values of investments as of December 31, 2020 and 2019, respectively:
December 31, 2020Amortized
cost		Gross
unrealized
gains		Gross
unrealized
losses		Fair
value
(in thousands)
Investment securities, held-to-maturity:
U.S. government and government agencies and authorities$694 $43 $— $737 
Investment securities, available-for-sale:
U.S. government and government agencies and authorities53,953 51 (41)53,963 
Total investment securities$54,647 $94 $(41)$54,700 
December 31, 2019Amortized
cost		Gross
unrealized
gains		Gross
unrealized
losses		Fair
value
(in thousands)
Investment securities, held-to-maturity:
U.S. government and government agencies and authorities$663 $22 $— $685 
Investment securities, available-for-sale:
U.S. government and government agencies and authorities56,382 46 — 56,428 
Total investment securities$57,045 $68 $— $57,113 
Schedule of Amortized Cost and Fair Value of Debt Securities
The following table presents the amortized cost and fair value of debt securities as of September 30, 2021, by contractual maturity:
September 30, 2021Held-to-maturityAvailable-for-sale
Amortized costFair valueAmortized costFair value
(in thousands)
Due within one year$305 $308 $21,139 $21,142 
Due after one year through five years15 16 141,835 141,352 
Due after five years through ten years265 256 4,961 4,831 
Due after ten years110 147 — — 
Total$695 $727 $167,935 $167,325 
The following tables present the amortized cost and fair value of debt securities as of December 31, 2020, by contractual maturity:
December 31, 2020Held-to-maturity Available-for-sale
Amortized
cost		Fair
value		Amortized
cost		Fair
value
(in thousands)
Due within one year
$265 $266 $— $— 
Due after one year through five years
319 328 43,382 43,431 
Due after five years through ten years
— — 10,571 10,532 
Due after ten years
110 143 — — 
Total
$694 $737 $53,953 $53,963 
Schedule of Net Investment Income
For the three and nine months ended September 30, 2021 and 2020, respectively, net investment income, which is included within other income in the Condensed Consolidated Statements of Operations and Comprehensive Loss, was derived from the following sources:
Three Months Ended
September 30,		Nine Months Ended
September 30,
2021202020212020
(in thousands)
Cash and cash equivalents$— $1 $— $108 
Short-term investments62 519 139 1,141 
Investment securities117 303 201 977 
Investment income, net$179 $823 $340 $2,226 
For the years ended December 31, 2020 and 2019, respectively, net investment income was derived from the following sources:
December 31,20202019
(in thousands)
Cash and cash equivalents
$108 $1,249 
Short-term investments
1,722 2,904 
Investment securities
1,146 386 
Net investment income
$2,976 $4,539 
Proceeds from Sales and Maturities of Investment Securities  
Proceeds from sales and maturities of investment securities and related gross realized gains (losses) included within net investment income were as follows for the years ended December 31, 2020 and 2019, respectively:
December 31,20202019
(in thousands)
Proceeds from sales of investment securities
$248,664 $269,205 
Proceeds from maturities of investment securities
63,751 55,635 
Gross realized gains
1,117 114 
Gross realized losses
(3)(3)
Net realized gains (losses)
$1,114 $111