Financial Information Related to Operations by Segment (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($) kT	Sep. 30, 2018 USD ($) kT	Sep. 30, 2019 USD ($) kT	Sep. 30, 2018 USD ($) kT	Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Revenue	$ 414,526	$ 381,499	$ 785,123	$ 775,255
Less: Joint Venture Revenue	(29,888)	(25,479)	(57,393)	(52,743)
Operating Earnings	116,863	108,104	201,624	208,989
Corporate General and Administrative Expense	(13,458)	(9,922)	(34,712)	(17,925)
Litigation Settlements and Losses				(1,800)
Other Non-Operating Income	942	428	1,142	999
Earnings Before Interest and Income Taxes	104,347	98,610	168,054	190,263
Interest Expense, Net	(10,137)	(6,817)	(18,983)	(13,449)
Earnings before Income Taxes	94,210	91,793	149,071	176,814
Capital Expenditures	37,387	40,371	62,875	93,444
Depreciation, Depletion, and Amortization	28,373	32,326	56,333	62,176
Identifiable Assets	2,326,211		2,326,211		$ 2,169,163
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	467,448	427,257	887,195	870,133
Operating Earnings	66,526	57,547	102,647	94,881
Operating Segments [Member] | Wholly-Owned [Member]
Segment Reporting Information [Line Items]
Operating Earnings	54,169	47,374	80,858	75,457
Operating Segments [Member] | Joint Venture [Member]
Segment Reporting Information [Line Items]
Operating Earnings	12,357	10,173	21,789	19,424
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(23,034)	(20,279)	(44,679)	(42,135)
Other [Member]
Segment Reporting Information [Line Items]
Identifiable Assets	78,088		78,088		37,434
Cement [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	$ 227,013	$ 193,161	$ 422,326	$ 379,949
Cement Sales Volume | kT	1,778	1,557	3,328	3,068
Operating Earnings	$ 66,526	$ 57,547	$ 102,647	$ 94,881
Capital Expenditures	8,209	14,220	18,746	33,833
Depreciation, Depletion, and Amortization	13,868	$ 12,746	28,086	$ 25,667
Identifiable Assets	$ 1,312,488		$ 1,312,488		1,289,468
Cement [Member] | Operating Segments [Member] | Wholly-Owned [Member]
Segment Reporting Information [Line Items]
Cement Sales Volume | kT	1,529	1,339	2,847	2,614
Cement [Member] | Operating Segments [Member] | Joint Venture [Member]
Segment Reporting Information [Line Items]
Cement Sales Volume | kT	249	218	481	454
Cement [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	$ (6,703)	$ (4,073)	$ (10,956)	$ (8,251)
Concrete and Aggregates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	55,971	39,744	95,749	80,584
Operating Earnings	7,255	4,100	11,689	9,584
Capital Expenditures	5,496	459	6,091	2,523
Depreciation, Depletion, and Amortization	2,754	2,052	4,945	4,105
Identifiable Assets	149,351		149,351		95,084
Concrete and Aggregates [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(407)	(501)	(784)	(832)
Gypsum Wallboard [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	128,660	129,609	255,384	272,024
Operating Earnings	38,456	45,671	76,388	96,151
Capital Expenditures	6,443	4,124	8,374	6,479
Depreciation, Depletion, and Amortization	5,147	5,201	10,099	10,031
Identifiable Assets	368,088		368,088		372,206
Paperboard [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	41,847	41,277	84,547	86,410
Operating Earnings	10,095	8,609	20,039	18,603
Capital Expenditures	17,239	5,345	29,599	6,410
Depreciation, Depletion, and Amortization	2,203	2,128	4,366	4,237
Identifiable Assets	159,457		159,457		138,614
Paperboard [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue	(15,924)	(15,705)	(32,939)	(33,052)
Oil and Gas Proppants [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue	13,957	23,466	29,189	51,166
Operating Earnings	(5,469)	(7,823)	(9,139)	(10,230)
Capital Expenditures		14,917	65	42,866
Depreciation, Depletion, and Amortization	3,803	9,851	7,642	17,446
Identifiable Assets	258,739		258,739		$ 236,357
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Capital Expenditures		1,306		1,333
Depreciation, Depletion, and Amortization	$ 598	$ 348	$ 1,195	$ 690