Basis of Presentation and Summary of Significant Accounting Policies - Changes in the Balance of Each Component of Accumulated Other Comprehensive Earnings (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
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance	$ 1,734,661	$ 1,604,212	$ 1,521,967	$ 1,584,707	$ 1,520,752	$ 1,413,514	$ 1,521,967	$ 1,413,514
Other comprehensive earnings (loss)	27,674	18,701	30,030	80,293	(7,843)	(12,671)	76,405	59,779
Ending balance	1,874,176	1,734,661	1,604,212	1,748,350	1,584,707	1,520,752	1,874,176	1,748,350
Balance of securities for which an allowance for credit losses has been recognized in net earnings	1,715			1,813			1,715	1,813
Unrealized Gains and Losses on Available-for-Sale Securities
Changes in the balance of each component of accumulated other comprehensive earnings (loss)
Beginning balance	(124,992)		$ (173,723)	(186,817)		$ (166,303)	(173,723)	(166,303)
Other comprehensive earnings before reclassifications	29,431			79,210			77,253	57,364
Amounts reclassified from accumulated other comprehensive earnings	(1,757)			1,083			(848)	2,415
Other comprehensive earnings (loss)	27,674			80,293			76,405	59,779
Ending balance	$ (97,318)	$ (124,992)		$ (106,524)	$ (186,817)		$ (97,318)	$ (106,524)