Investments - Gains (Losses) Related to Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Net gains recognized during the period	$ 1,853	$ 12,904	$ 14,459	$ 5,304
Less: net gains recognized during the period on equity securities sold during the period	2,902	18,929	19,623	25,005
Unrealized (losses) recognized during the period on equity securities held	$ (1,049)	$ (6,025)	$ (5,164)	$ (19,701)