Investments - Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Net (losses) gains recognized during the period on equity securities	$ (18,002)	$ 2,109
Less: Net losses recognized during the period on equity securities sold during the period	(16,352)	0
Unrealized (losses) gains recognized during the period on equity securities still held at the end of the period	$ (1,650)	$ 2,109