Debt (Narratives) (Details) - USD ($)	3 Months Ended			6 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	May 04, 2021	Mar. 31, 2021
Debt Disclosure [Abstract]
Long-term Debt	$ 750,000,000			$ 750,000,000			$ 545,000,000
Line of Credit Facility [Line Items]
Maximum availability under New Revolving Credit Facility	100,000,000			100,000,000
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000			100,000,000
Outstanding borrowings	443,875,000			443,875,000
Current portion of long term debt and finance lease obligations	60,515,000			60,515,000			4,450,000
Deferred Costs	14,690,000			14,690,000
Accumulated Amortization, Deferred Finance Costs	463,000			463,000			8,744,000
Unsecured credit lines	$ 2,547,000			2,547,000
Amount drawn on unsecured credit lines				0
Stock Issued During Period, Shares, New Issues	4,312,500	4,312,500
Common Stock, Par or Stated Value Per Share						$ 48.00
Proceeds from Issuance or Sale of Equity				$ 207,000,000	$ 0
Lessee, Finance Lease, Term of Contract	23 years			23 years
Operating Income (Loss)	$ 23,660,000		$ 15,820,000	$ 34,406,000	17,609,000
Secured Debt	450,000,000			450,000,000			445,000,000
Long-term Debt	750,000,000			750,000,000			545,000,000
Extinguishment of Debt, Amount	0		$ 0	14,803,000	$ 0
Short-term Debt	60,000,000			60,000,000
Debt Instrument, Periodic Payment, Principal	6,125,000
Debt Instrument, Periodic Payment	1,125,000
Dorner
Line of Credit Facility [Line Items]
Operating Income (Loss)	3,161,000			4,324,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt Issuance Costs, Gross	977,000			977,000
Revolving Credit Facility [Member] | Dorner
Line of Credit Facility [Line Items]
Debt Issuance Costs, Gross	3,050,000			3,050,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Accumulated Amortization, Deferred Finance Costs	403,000			403,000			2,313,000
Extinguishment of Debt, Amount	326,000
Debt Issuance Costs, Gross	4,027,000			4,027,000			$ 3,615,000
Required payments [Member]
Line of Credit Facility [Line Items]
Current portion of long term debt and finance lease obligations	4,500,000			4,500,000
Secured Debt
Line of Credit Facility [Line Items]
Extinguishment of Debt, Amount	5,946,000
Debt Issuance Costs, Gross	5,432,000			5,432,000
Bridge Loan
Line of Credit Facility [Line Items]
Extinguishment of Debt, Amount	8,531,000
New Revolving Credit Facility
Line of Credit Facility [Line Items]
Outstanding letters of credit	17,196,000			17,196,000
New Revolving Credit Facility | Standby Letters of Credit
Line of Credit Facility [Line Items]
Outstanding letters of credit	16,495,000			16,495,000
New Revolving Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Outstanding letters of credit	701,000			701,000
New Revolving Credit Facility | Unsecured Lines of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	15,651,000			15,651,000
Outstanding borrowings	$ 12,911,000			$ 12,911,000