Business Combinations (Details) $ / shares in Units, $ in Thousands, T in Millions		6 Months Ended
	Sep. 18, 2020 USD ($) $ / shares	Jun. 30, 2021 USD ($)	Sep. 30, 2021 T
Business Acquisition [Line Items]
Processing capacity | T			7.1
Cash	$ 309
Accounts receivable	75
Inventory	2,459
Prepaid expenses and other current assets	124
Property, plant and equipment	60,310
Right-of-use assets	9,603
Total assets acquired	72,880
Accounts payable	16
Business Combination, Liabilities Assumed, Accrued Expense and Other Liabilities	2,008
Asset retirement obligations	8,424
Operating lease liabilities	9,603
Deferred income taxes	11,149
Total liabilities assumed	31,200
Estimated fair value of net assets acquired	41,680
Business Combination, Bargain Purchase, Gain Recognized, Amount	39,600
Eagle Materials Holdings [Member]
Business Acquisition [Line Items]
Base price consideration	$ 2,000
Business Acquisition, Volume Weighted Average Share Price | $ / shares	$ 1.33
Business Acquisition, Share Price | $ / shares	$ 1.37
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 2,060
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Working Capital	20
Total purchase consideration	$ 2,080
Shares issued	1,504
Business Combination, Acquisition Related Costs		$ 891
Eagle Materials Holdings [Member] | BNSF [Member]
Business Acquisition [Line Items]
Processing capacity | T			1.6