Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Comprehensive income (loss) (pretax):
Pretax earnings	$ 271,579	$ 102,700	$ 667,623	$ 614,822
Comprehensive income (loss) (tax effect):
Net earnings (Tax)	257,315	(37,472)	112,117	(225,946)
Comprehensive income (loss) (net of tax):
Net earnings	528,894	65,228	779,740	388,876
Other comprehensive income (loss):
Foreign currency translation (pretax)	(1,794)	(5,821)	19,240	(7,803)
Foreign currency translation (tax effect)
Foreign currency translation (net of tax)	(1,794)	(5,821)	19,240	(7,803)
Unrealized gain (loss) on investments (pretax)	4,388	4,238	30,492	64,856
Unrealized gain (loss) on investments (tax effect)	(1,536)	(1,483)	(10,672)	(22,700)
Unrealized gain (loss) on investments (net of tax)	2,852	2,755	19,820	42,156
Change in fair value of cash flow hedges (pretax)	911	2,853	3,655	8,039
Change in fair value of cash flow hedges (tax effect)	(346)	(931)	(1,390)	(2,901)
Change in fair value of cash flow hedges (net of tax)	565	1,922	2,265	5,138
Total comprehensive income (loss) (pretax)	275,084	103,970	721,010	679,914
Total comprehensive income (loss) (tax effect)	255,433	(39,886)	100,055	(251,547)
Total comprehensive income (loss) (net of tax)	$ 530,517	$ 64,084	$ 821,065	$ 428,367