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Investments - Gains and proceeds (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments
Realized loss (gain) on sale of investments	$ 0	$ (100)		$ (100)
Maturities of investments - debt securities			$ 9,000	7,000
Proceeds from sale of available-for-sale debt securities			1,200	4,000
Purchases of available-for-sale securities			58,900
Maximum
Investments
Realized loss (gain) on sale of investments			$ (100)
Purchases of available-for-sale securities				$ 100