Financial Instruments - Summary of Bond Activity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available for Sale [Roll Forward]
Fair value at beginning of period	$ 60,659	$ 56,556
Purchases	3,447	27,216
Sales	(22,078)	(1,686)
Maturities and calls	(15,409)	(22,272)
Decrease in bond premium	(857)	(460)
Fair market value adjustment	(54)	1,305
Fair value at end of period	$ 25,708	$ 60,659

Available For Sale Securities Debt Securities Fair Market Value Adjustment

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of cash outflow to acquire investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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