Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Comprehensive income (loss) (pretax):
Net earnings	$ 477,529	$ 637,613	$ 628,358
Comprehensive income (loss) (tax effect):
Net earnings	(106,672)	152,970	(229,934)
Comprehensive income (loss) (net of tax):
Net earnings	370,857	790,583	398,424
Other comprehensive income (loss):
Foreign currency translation (pretax)	(1,759)	14,652	(5,862)
Foreign currency translation (tax effect)
Foreign currency translation (net of tax)	(1,759)	14,652	(5,862)
Unrealized gain (loss) on investments (pretax)	(76,124)	30,929	13,822
Unrealized gain (loss) on investments (tax effect)	16,356	(10,825)	(4,838)
Unrealized gain (loss) on investments (net of tax)	(59,768)	20,104	8,984
Change in fair value of cash flow hedges (pretax)	633	4,445	9,916
Change in fair value of cash flow hedges (tax effect)	(156)	(1,363)	(3,767)
Change in fair value of cash flow hedges (net of tax)	477	3,082	6,149
Postretirement benefit obligation gain (loss) (pretax)	(1,359)	288	28
Postretirement benefit obligation gain (loss) (tax effect)	334	(253)	(10)
Postretirement benefit obligation gain (loss) (net of tax)	(1,025)	35	18
Total comprehensive income (loss) (pretax)	398,920	687,927	646,262
Total comprehensive income (loss) (tax effect)	(90,138)	140,529	(238,549)
Total comprehensive income (loss) (net of tax)	$ 308,782	$ 828,456	$ 407,713