Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock:	Additional paid-in capital:	Accumulated other comprehensive income:	Unrealized gains (losses) on non-impaired securities:	Unrealized losses on impaired held-to-maturity securities:	Unrealized losses on impaired available-for-sale securities:	Unrealized losses on impaired available-for-sale securities: Cumulative Effect, Period of Adoption, Adjustment	Foreign currency translation adjustments:	Benefit plan liability adjustment:	Retained earnings:	Retained earnings: Cumulative Effect, Period of Adoption, Adjusted Balance	Retained earnings: Cumulative Effect, Period of Adoption, Adjustment
Stockholders’ equity, beginning of period at Dec. 31, 2019		$ 36	$ 41,716		$ 70,665	$ (4)	$ (2)	$ 2	$ 5,101	$ (15,652)		$ 2,014,570	$ (3,032)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period	$ 352,561				348,076
Amortization						4
Change in shadow deferred policy acquisition costs						(2)
Disposals of previously impaired securities						2
Change in translation adjustments during period	14								15
Amortization of net prior service cost and net gain (loss), net of tax	(12,784)									(12,784)
Net earnings	92,312										$ 92,312
Stockholder dividends											(1,273)
Stockholders’ equity, end of period at Dec. 31, 2020	2,539,750	36	41,716	$ 395,421	418,741	0	0	0	5,116	(28,436)	2,102,577	2,102,577	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period	(179,587)				(192,521)
Amortization						0
Change in shadow deferred policy acquisition costs						0
Disposals of previously impaired securities						0
Change in translation adjustments during period	(16)								(16)
Amortization of net prior service cost and net gain (loss), net of tax	13,069									13,069
Net earnings	180,681										180,681
Stockholder dividends											(1,272)
Stockholders’ equity, end of period at Dec. 31, 2021	2,539,691	36	41,716	215,953	226,220	0	0	$ 0	5,100	(15,367)	2,281,986	$ 2,281,986	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) during period	(642,148)				(646,185)
Amortization						0
Change in shadow deferred policy acquisition costs						0
Disposals of previously impaired securities						0
Change in translation adjustments during period	407								407
Amortization of net prior service cost and net gain (loss), net of tax	13,428									13,428
Net earnings	101,144										101,144
Stockholder dividends											(1,274)
Stockholders’ equity, end of period at Dec. 31, 2022	$ 2,007,211	$ 36	$ 41,716	$ (416,397)	$ (419,965)	$ 0	$ 0		$ 5,507	$ (1,939)	$ 2,381,856