Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Comprehensive income (loss) (pretax):
Net earnings	$ 1,217,923	$ 1,475,497	$ 796,658
Comprehensive income (loss) (tax effect):
Net earnings	(294,925)	(352,211)	(185,802)
Comprehensive income (loss) (net of tax):
Net earnings	922,998	1,123,286	610,856
Other comprehensive income (loss):
Foreign currency translation (pretax)	(782)	(2,828)	(5,694)
Foreign currency translation (tax effect)	0	0	0
Foreign currency translation (net of tax)	(782)	(2,828)	(5,694)
Unrealized gain (loss) on investments (pretax)	(405,144)	(78,452)	96,170
Unrealized gain (loss) on investments (tax effect)	85,954	15,826	(19,201)
Unrealized gain (loss) on investments (net of tax)	(319,190)	(62,626)	76,969
Change in fair value cash flow hedges (pretax)	6,672	605	(569)
Change in fair value of cash flow hedges (tax effect)	(1,639)	(148)	140
Change in fair value of cash flow hedges, (net of tax)	5,033	457	(429)
Amounts reclassified into earnings on hedging activities, (pre tax)	(772)	3,948	3,640
Amounts reclassified into earnings on hedging activities (tax effect)	190	(970)	(894)
Amounts reclassified into earnings on hedging,( net of tax)	(582)	2,978	2,746
Postretirement benefit obligation gain (loss) (pretax)	2,772	2,049	(1,838)
Postretirement benefit obligation gain (loss) (tax effect)	(681)	(503)	451
Postretirement benefit obligation gain (loss) (net of tax)	2,091	1,546	(1,387)
Total other comprehensive income (loss) (pretax)	(397,254)	(74,678)	91,709
Total other comprehensive income (loss) (tax effect)	83,824	14,205	(19,504)
Total other comprehensive income loss, net	(313,430)	(60,473)	72,205
Total comprehensive income (pretax)	820,669	1,400,819	888,367
Total comprehensive income (tax effect)	(211,101)	(338,006)	(205,306)
Total comprehensive income (loss) ( net of tax)	$ 609,568	$ 1,062,813	$ 683,061