Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Comprehensive income (loss) (pretax):
Net earnings	$ 537,522	$ 408,487	$ 325,636
Comprehensive income (loss) (tax effect):
Net earnings	(195,131)	(143,779)	(120,269)
Comprehensive income (loss) (net of tax):
Net earnings	342,391	264,708	205,367
Other comprehensive income (loss):
Foreign currency translation (pretax)	(9,134)	(1,271)	(2,854)
Foreign currency translation (tax effect)	0	0	0
Foreign currency translation (net of tax)	(9,134)	(1,271)	(2,854)
Unrealized gain (loss) on investments (pretax)	(51,590)	29,099	15,094
Unrealized gain (loss) on investments (tax effect)	17,936	(10,320)	(5,089)
Unrealized gain (loss) on investments (net of tax)	(33,654)	18,779	10,005
Change in fair value of cash flow hedges (pretax)	19,317	9,405	(9,179)
Change in fair value of cash flow hedges (tax effect)	(7,340)	(3,574)	3,488
Change in fair value of cash flow hedges (net of tax)	11,977	5,831	(5,691)
Postretirement benefit obligation gain (loss) (pretax)	(697)	(974)	(692)
Postretirement benefit obligation gain (loss) (tax effect)	265	391	263
Postretirement benefit obligation gain (loss) (net of tax)	(432)	(583)	(429)
Total comprehensive income (loss) (pretax)	495,418	444,746	328,005
Total comprehensive income (loss) (tax effect)	(184,270)	(157,282)	(121,607)
Total comprehensive income (loss) (net of tax)	$ 311,148	$ 287,464	$ 206,398