Summary of Significant Accounting Policies - Schedule of Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment Out of Accumulated Other Comprehensive Income
Net realized gains (losses)	$ 36,463		$ (2,109)		$ 50,613	$ 13,043
Earnings before income taxes	102,021		114,879		191,855	35,515
Income tax expense	(20,206)		(22,713)		(37,028)	(4,616)
Net earnings	81,815	$ 73,012	92,166	$ (61,267)	154,827	30,899
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out of Accumulated Other Comprehensive Income
Net realized gains (losses)	366		312		1,549	2,618
Credit losses on available-for-sale securities	171		(107)		193	(956)
Earnings before income taxes	537		205		1,742	1,662
Income tax expense	(113)		(43)		(366)	(349)
Net earnings	$ 424		$ 162		$ 1,376	$ 1,313