Consolidated Statements of Comprehensive Earnings - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Earnings	$ 256,632	$ 198,219	$ 152,592
Net Actuarial Change in Defined Benefit Plans:
Unrealized gain (loss) during the period, net of tax (expense) benefit of ($1,995), ($1,544) and $488	3,407	2,765	(613)
Amortization of net actuarial loss, net of tax benefit of $301, $760 and $242	955	1,248	1,271
Reclassification of Income Tax Effects to Retained Earnings	(978)
Comprehensive Earnings	$ 260,016	$ 202,232	$ 153,250