Fair Value of Derivative and Other Financial Instruments - Investments in NDT and Gross Realized Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Equity securities:
Net gains (losses) from equity securities sold	$ (189)	$ (2,210)	$ 1,758	$ 1,735
Net gains (losses) from equity securities still held	(4,946)	(4,061)	3,673	(52,320)
Total net gains (losses) on equity securities	(5,135)	(6,271)	5,431	(50,585)
Available-for-sale debt securities:
Net (losses) on debt securities	(3,269)	(9,465)	(3,616)	(33,519)
Net gains (losses) on investment securities	$ (8,404)	$ (15,736)	$ 1,815	$ (84,104)