Basis of Presentation and Summary of Significant Accounting Policies - Effects of Reclassifications out of Accumulated Other Comprehensive Earnings (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Earnings before income taxes	$ 157,245			$ 116,825			$ 392,391	$ 380,119
Income tax (expense) benefit	(32,635)			(21,798)			(80,231)	(75,200)
Net earnings	124,610	$ 124,336	$ 63,214	95,027	$ 81,992	$ 127,900	312,160	304,919
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Net realized gains (losses) - Available-for-sale	2,878			(1,365)			1,775	(3,129)
Credit gains (losses) presented within net realized gains	(654)			(6)			(702)	72
Earnings before income taxes	2,224			(1,371)			1,073	(3,057)
Income tax (expense) benefit	(467)			288			(225)	642
Net earnings	$ 1,757			$ (1,083)			$ 848	$ (2,415)