Consolidated Statements of Comprehensive Earnings (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Earnings	$ 72,603	$ 63,362	$ 138,942	$ 118,244
Net Actuarial Change in Defined Benefit Plans:
Amortization of net actuarial loss	73	314	146	628
Tax expense	(17)	(117)	(34)	(234)
Comprehensive Earnings	$ 72,659	$ 63,559	$ 139,054	$ 118,638