Marketable Securities - Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net investment income
Gross investment income from debt securities available-for-sale	$ 1,084	$ 89	$ 1,224	$ 161
Investment expenses	(57)	(24)	(75)	(76)
Net investment income (excluding net realized capital gains or losses)	1,027	65	1,149	85
Net realized capital (losses) gains	(157)	0	(160)	19
Net investment income	$ 870	$ 65	$ 989	$ 104

Investment Income, Excluding Realized Gain (Loss)

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Amount before accretion (amortization) of purchase discount (premium) of interest income and dividend income on nonoperating securities.

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Amount of expenses related to the generation of investment income.

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Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

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