Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Comprehensive income (loss) (pretax):
Pretax earnings	$ 840,177	$ 1,219,397	$ 1,476,573
Comprehensive income (loss) (tax effect):
Income tax expense	211,470	294,925	352,211
Comprehensive income (loss) (net of tax):
Earnings available to common stockholders	628,707	924,472	1,124,362
Other comprehensive income (loss):
Foreign currency translation (pretax)	2,832	782	2,828
Foreign currency translation (tax effect)	0	0	0
Foreign currency translation (net of tax)	2,832	782	2,828
Unrealized gain (loss) on investments (pretax)	70,703	367,533	57,885
Unrealized gain (loss) on investments (tax effect)	(14,846)	(78,056)	(11,507)
Unrealized gain (loss) on investments (net of tax)	55,857	289,477	46,378
Change in fair value cash flow hedges (pretax)	8,497	6,672	605
Change in fair value of cash flow hedges (tax effect)	(2,087)	(1,639)	(148)
Change in fair value of cash flow hedges, (net of tax)	6,410	5,033	457
Amounts reclassified into earnings on hedging activities (pre tax)	5,417	772	3,948
Amounts reclassified into earnings on hedging activities (tax effect)	(1,330)	(190)	(970)
Amounts reclassified into earnings on hedging activities (net of tax)	4,087	582	2,978
Postretirement benefit obligation gain (loss) (pretax)	1,849	2,772	2,049
Postretirement benefit obligation gain (loss) (tax effect)	(454)	(681)	(503)
Postretirement benefit obligation gain (loss) (net of tax)	1,395	2,091	1,546
Total other comprehensive income (loss) (pretax)	78,464	359,643	54,111
Total other comprehensive income (loss) (tax effect)	(16,057)	(75,926)	(9,886)
Total other comprehensive income (loss) (net of tax)	62,407	283,717	44,225
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	918,641	859,754	1,422,462
Other comprehensive income (loss) tax effect	(227,527)	(218,999)	(342,325)
Total comprehensive income (loss) (net of tax)	$ 691,114	$ 640,755	$ 1,080,137