Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Comprehensive income (loss) (pretax):
Net earnings	$ 796,658	$ 378,124	$ 477,529
Comprehensive income (loss) (tax effect):
Net earnings	(185,802)	63,924	(106,672)
Comprehensive income (loss) (net of tax):
Net earnings	610,856	442,048	370,857
Other comprehensive income (loss):
Foreign currency translation (pretax)	(5,694)	9,377	(1,759)
Foreign currency translation (tax effect)	0	0	0
Foreign currency translation (net of tax)	(5,694)	9,377	(1,759)
Unrealized gain (loss) on investments (pretax)	96,170	124,566	(76,124)
Unrealized gain (loss) on investments (tax effect)	(19,201)	(26,623)	16,356
Unrealized gain (loss) on investments (net of tax)	76,969	97,943	(59,768)
Change in fair value of cash flow hedges (pretax)	(569)	(8,352)	598
Change in fair value of cash flow hedges (tax effect)	140	2,051	(147)
Change in fair value of cash flow hedges (net of tax)	(429)	(6,301)	451
Amounts reclassified into earnings on hedging activities, (pre tax)	3,640	(3)	35
Amounts reclassified into earnings on hedging activities (tax effect)	(894)	1	(9)
Amounts reclassified into earnings on hedging,( net of tax)	2,746	(2)	26
Postretirement benefit obligation gain (loss) (pretax)	(1,838)	441	(1,359)
Postretirement benefit obligation gain (loss) (tax effect)	451	(108)	334
Postretirement benefit obligation gain (loss) (net of tax)	(1,387)	333	(1,025)
Total other comprehensive income (loss) (pretax)	91,709	126,029	(78,609)
Total other comprehensive income (loss) (tax effect)	(19,504)	(24,679)	16,534
Total other comprehensive income loss, net	72,205	101,350	(62,075)
Total comprehensive income	888,367	504,153	398,920
Total comprehensive income, tax	(205,306)	39,245	(90,138)
Total comprehensive income, net	$ 683,061	$ 543,398	$ 308,782