Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock:	Additional paid-in capital:	Accumulated other comprehensive income (loss):	Unrealized gains (losses) on debt securities available-for-sale:	Foreign currency translation adjustments:	Benefit plan liability adjustment:	Retained earnings:
Total stockholders’ equity, beginning of period at Dec. 31, 2020		$ 36	$ 41,716		$ 418,741	$ 5,116	$ (28,436)	$ 2,102,577
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period, net of tax	$ (110,799)				(115,728)
Change in translation adjustments during period						(76)
Amortization of net prior service cost and net gain, net of tax	3,870						3,870
Net earnings	112,028							112,028
Total stockholders’ equity, end of period at Jun. 30, 2021	2,539,844	36	41,716	$ 283,487	303,013	5,040	(24,566)	2,214,605
Total stockholders’ equity, beginning of period at Mar. 31, 2021		36	41,716		265,427	5,111	(26,501)	2,164,706
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period, net of tax	41,396				37,586
Change in translation adjustments during period						(71)
Amortization of net prior service cost and net gain, net of tax	1,935						1,935
Net earnings	49,899							49,899
Total stockholders’ equity, end of period at Jun. 30, 2021	2,539,844	36	41,716	283,487	303,013	5,040	(24,566)	2,214,605
Total stockholders’ equity, beginning of period at Dec. 31, 2021	2,539,691	36	41,716		226,220	5,100	(15,367)	2,281,986
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period, net of tax	(509,523)				(513,650)
Change in translation adjustments during period						291
Amortization of net prior service cost and net gain, net of tax	2,268						2,268
Net earnings	66,949							66,949
Total stockholders’ equity, end of period at Jun. 30, 2022	2,095,549	36	41,716	(295,138)	(287,430)	5,391	(13,099)	2,348,935
Total stockholders’ equity, beginning of period at Mar. 31, 2022		36	41,716		(53,121)	5,413	(14,233)	2,318,170
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period, net of tax	(232,914)				(234,309)
Change in translation adjustments during period						(22)
Amortization of net prior service cost and net gain, net of tax	1,134						1,134
Net earnings	30,765							30,765
Total stockholders’ equity, end of period at Jun. 30, 2022	$ 2,095,549	$ 36	$ 41,716	$ (295,138)	$ (287,430)	$ 5,391	$ (13,099)	$ 2,348,935