Condensed Consolidating Statement of Earnings and Comprehensive Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Revenue	$ 381,499	$ 376,315	$ 775,255	$ 742,436
Cost of Goods Sold	283,568	279,561	585,690	559,623
Gross Profit	97,931	96,754	189,565	182,813
Equity in Earnings of Unconsolidated Joint Venture	10,173	11,955	19,424	21,831
Corporate General and Administrative Expense	(9,922)	(9,821)	(17,925)	(19,500)
Legal Settlements			(1,800)
Other Non-Operating Income	428	887	999	1,644
Interest Expense, net	(6,817)	(7,456)	(13,449)	(14,939)
Earnings before Income Taxes	91,793	92,319	176,814	171,849
Income Taxes	(19,190)	(28,957)	(37,872)	(53,605)
Net Earnings	72,603	63,362	138,942	118,244	$ 256,632
Net Actuarial Change in Benefit Plans, net of tax	56	197	112	394
Comprehensive Earnings	72,659	63,559	139,054	118,638
Eliminations [Member]
Equity in Earnings of Unconsolidated Joint Venture	(10,173)	(11,955)	(19,424)	(21,831)
Equity in Earnings of Subsidiaries	(75,030)	(64,496)	(142,288)	(122,792)
Earnings before Income Taxes	(85,203)	(76,451)	(161,712)	(144,623)
Net Earnings	(85,203)	(76,451)	(161,712)	(144,623)
Net Actuarial Change in Benefit Plans, net of tax	(56)	(197)	(112)	(394)
Comprehensive Earnings	(85,259)	(76,648)	(161,824)	(145,017)
Parent [Member]
Equity in Earnings of Unconsolidated Joint Venture	10,173	11,955	19,424	21,831
Equity in Earnings of Subsidiaries	75,030	64,496	142,288	122,792
Corporate General and Administrative Expense	(9,090)	(9,178)	(15,819)	(17,826)
Other Non-Operating Income	(126)	(179)	(219)	(346)
Interest Expense, net	(6,806)	(13,833)	(13,424)	(26,795)
Earnings before Income Taxes	69,181	53,261	132,250	99,656
Income Taxes	3,421	10,101	6,692	18,588
Net Earnings	72,602	63,362	138,942	118,244
Net Actuarial Change in Benefit Plans, net of tax	56	197	112	394
Comprehensive Earnings	72,658	63,559	139,054	118,638
Guarantor Subsidiaries [Member]
Revenue	381,499	376,315	775,255	742,436
Cost of Goods Sold	283,568	279,561	585,690	559,623
Gross Profit	97,931	96,754	189,565	182,813
Equity in Earnings of Unconsolidated Joint Venture	10,173	11,955	19,424	21,831
Corporate General and Administrative Expense	(832)	(643)	(2,106)	(1,674)
Legal Settlements			(1,800)
Other Non-Operating Income	554	1,066	1,218	1,990
Interest Expense, net	(11)	6,377	(25)	11,856
Earnings before Income Taxes	107,815	115,509	206,276	216,816
Income Taxes	(22,611)	(39,058)	(44,564)	(72,193)
Net Earnings	85,204	76,451	161,712	144,623
Net Actuarial Change in Benefit Plans, net of tax	56	197	112	394
Comprehensive Earnings	$ 85,260	$ 76,648	$ 161,824	$ 145,017