Investments - Equity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Net (losses) gains recognized during the period on equity securities	$ (8,482)	$ 36,377	$ (26,484)	$ 38,486
Less: Net losses recognized during the period on equity securities sold during the period	(27,310)	0	(43,662)	0
Unrealized gains recognized during the period on equity securities still held at the end of the period	$ 18,828	$ 36,377	$ 17,178	$ 38,486