Investments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Net realized gains (losses) on investments	$ 53,800	$ 63,352	$ (12,715)	$ (2,089)
Proceeds from sales of investment real estate		0	10,537	0
Realized gains on sales of investment real estate		$ 0	$ 1,213	$ 0