Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Comprehensive income (loss) (pretax):
Net earnings	$ 768,911	$ 561,418	$ 537,522
Comprehensive income (loss) (tax effect):
Net earnings	(279,910)	(204,677)	(195,131)
Comprehensive income (loss) (net of tax):
Net earnings	489,001	356,741	342,391
Other comprehensive income (loss):
Foreign currency translation (pretax)	$ (4,473)	$ (19,883)	$ (9,134)
Foreign currency translation (tax effect)
Foreign currency translation (net of tax)	$ (4,473)	$ (19,883)	$ (9,134)
Unrealized gain (loss) on investments (pretax)	(41,639)	54,139	(51,590)
Unrealized gain (loss) on investments (tax effect)	14,573	(18,949)	17,936
Unrealized gain (loss) on investments (net of tax)	(27,066)	35,190	(33,654)
Change in fair value of cash flow hedges (pretax)	9,721	8,203	19,317
Change in fair value of cash flow hedges (tax effect)	(3,694)	(3,117)	(7,340)
Change in fair value of cash flow hedges (net of tax)	6,027	5,086	11,977
Postretirement benefit obligation gain (loss) (pretax)	(1,029)	(1,325)	(697)
Postretirement benefit obligation gain (loss) (tax effect)	381	490	265
Postretirement benefit obligation gain (loss) (net of tax)	(648)	(835)	(432)
Total comprehensive income (loss) (pretax)	731,491	602,552	495,418
Total comprehensive income (loss) (tax effect)	(268,650)	(226,253)	(184,270)
Total comprehensive income (loss) (net of tax)	$ 462,841	$ 376,299	$ 311,148