Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Comprehensive income (loss) (pretax):
Net earnings	$ 561,418	$ 537,522	$ 408,487
Comprehensive income (loss) (tax effect):
Net earnings	(204,677)us-gaap_IncomeTaxExpenseBenefit	(195,131)us-gaap_IncomeTaxExpenseBenefit	(143,779)us-gaap_IncomeTaxExpenseBenefit
Comprehensive income (loss) (net of tax):
Net earnings	356,741us-gaap_NetIncomeLoss	342,391us-gaap_NetIncomeLoss	264,708us-gaap_NetIncomeLoss
Other comprehensive income (loss):
Foreign currency translation (pretax)	(19,883)	(9,134)	(1,271)
Foreign currency translation (tax effect)	0	0	0
Foreign currency translation (net of tax)	(19,883)	(9,134)	(1,271)
Unrealized gain (loss) on investments (pretax)	54,139	(51,590)	29,099
Unrealized gain (loss) on investments (tax effect)	(18,949)	17,936	(10,320)
Unrealized gain (loss) on investments (net of tax)	35,190	(33,654)	18,779
Change in fair value of cash flow hedges (pretax)	8,203	19,317	9,405
Change in fair value of cash flow hedges (tax effect)	(3,117)	(7,340)	(3,574)
Change in fair value of cash flow hedges (net of tax)	5,086	11,977	5,831
Postretirement benefit obligation gain (loss) (pretax)	(1,325)	(697)	(974)
Postretirement benefit obligation gain (loss) (tax effect)	490	265	391
Postretirement benefit obligation gain (loss) (net of tax)	(835)	(432)	(583)
Total comprehensive income (loss) (pretax)	602,552	495,418	444,746
Total comprehensive income (loss) (tax effect)	(226,253)us-gaap_OtherComprehensiveIncomeLossTax	(184,270)us-gaap_OtherComprehensiveIncomeLossTax	(157,282)us-gaap_OtherComprehensiveIncomeLossTax
Total comprehensive income (loss) (net of tax)	$ 376,299us-gaap_ComprehensiveIncomeNetOfTax	$ 311,148us-gaap_ComprehensiveIncomeNetOfTax	$ 287,464us-gaap_ComprehensiveIncomeNetOfTax

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