Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Comprehensive income (loss) (pretax):
Net earnings	$ 628,358	$ 768,911	$ 561,418
Comprehensive income (loss) (tax effect):
Net earnings	(229,934)	(279,910)	(204,677)
Comprehensive income (loss) (net of tax):
Net earnings	398,424	489,001	356,741
Other comprehensive income (loss):
Foreign currency translation (pretax)	(5,862)	(4,473)	(19,883)
Foreign currency translation (tax effect)
Foreign currency translation (net of tax)	(5,862)	(4,473)	(19,883)
Unrealized gain (loss) on investments (pretax)	13,822	(41,639)	54,139
Unrealized gain (loss) on investments (tax effect)	(4,838)	14,573	(18,949)
Unrealized gain (loss) on investments (net of tax)	8,984	(27,066)	35,190
Change in fair value of cash flow hedges (pretax)	9,916	9,721	8,203
Change in fair value of cash flow hedges (tax effect)	(3,767)	(3,694)	(3,117)
Change in fair value of cash flow hedges (net of tax)	6,149	6,027	5,086
Postretirement benefit obligation gain (loss) (pretax)	28	(1,029)	(1,325)
Postretirement benefit obligation gain (loss) (tax effect)	(10)	381	490
Postretirement benefit obligation gain (loss) (net of tax)	18	(648)	(835)
Total comprehensive income (loss) (pretax)	646,262	731,491	602,552
Total comprehensive income (loss) (tax effect)	(238,549)	(268,650)	(226,253)
Total comprehensive income (loss) (net of tax)	$ 407,713	$ 462,841	$ 376,299