Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Comprehensive income (loss) (pretax):
Net earnings	$ 216,848	$ 172,209	$ 395,896	$ 299,597
Comprehensive income (loss) (tax effect):
Net earnings	(78,857)	(62,789)	(144,937)	(109,608)
Comprehensive income (loss) (net of tax):
Net earnings	137,991	109,420	250,959	189,989
Other comprehensive income (loss):
Foreign currency translation (pretax)	1,557	3,459	(2,205)	1,530
Foreign currency translation (tax effect)	0	0	0	0
Foreign currency translation (net of tax)	1,557	3,459	(2,205)	1,530
Unrealized net gain (loss) on investments (pretax)	(41,095)	10,673	(41,006)	12,546
Unrealized net gain (loss) on investments (tax effect)	14,322	(3,769)	14,254	(4,349)
Unrealized net gain (loss) on investments (net of tax)	(26,773)	6,904	(26,752)	8,197
Change in fair value of cash flow hedges (pretax)	1,946	768	12,142	253
Change in fair value of cash flow hedges (tax effect)	(740)	(292)	(4,614)	(96)
Change in fair value of cash flow hedges (net of tax)	1,206	476	7,528	157
Total comprehensive income (loss) (pretax)	179,256	187,109	364,827	313,926
Total comprehensive income (loss) (tax effect)	(65,275)	(66,850)	(135,297)	(114,053)
Total comprehensive income (loss) (net of tax)	$ 113,981	$ 120,259	$ 229,530	$ 199,873