Long-Term Debt (Schedule of debt) (detail) (USD $)	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Debt Instrument [Line Items]
Long-term Debt	$ 274,164,000us-gaap_LongTermDebt	$ 218,516,000us-gaap_LongTermDebt
Total	274,164,000us-gaap_LongTermDebt	218,516,000us-gaap_LongTermDebt
Current Portion of Long-Term Debt	2,530,000us-gaap_LongTermDebtCurrent	2,277,000us-gaap_LongTermDebtCurrent
Long-Term Debt, Less Current Portion	271,634,000us-gaap_LongTermDebtNoncurrent	216,239,000us-gaap_LongTermDebtNoncurrent
Revolving credit facility [Member]
Debt Instrument [Line Items]
Long-term Debt	233,000,000	175,000,000
Long-term Debt, Weighted Average Interest Rate	1.92%	1.65%
Debt Instrument, Maturity Date	2017
Total	233,000,000	175,000,000
Secured Industrial Revenue Development Bonds [Member]
Debt Instrument [Line Items]
Long-term Debt	22,630,000	22,630,000
Long-term Debt, Weighted Average Interest Rate	2.97%	3.23%
Debt Instrument, Maturity Date	2029
Total	22,630,000	22,630,000
Secured Industrial Revenue Development Bond [Member]
Debt Instrument [Line Items]
Long-term Debt	1,398,000	1,500,000
Long-term Debt, Weighted Average Interest Rate	2.00%	2.00%
Debt Instrument, Maturity Date	2021
Total	1,398,000	1,500,000
Secured promissory note 1 [Member]
Debt Instrument [Line Items]
Long-term Debt	13,769,000	15,313,000
Long-term Debt, Weighted Average Interest Rate	6.98%	6.98%
Debt Instrument, Maturity Date	2022
Total	13,769,000	15,313,000
Secured promissory note 2 [Member]
Debt Instrument [Line Items]
Long-term Debt	3,122,000	3,731,000
Long-term Debt, Weighted Average Interest Rate	6.35%	6.35%
Debt Instrument, Maturity Date	2020
Total	3,122,000	3,731,000
Other [Member]
Debt Instrument [Line Items]
Long-term Debt	245,000	342,000
Total	$ 245,000	$ 342,000

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20)

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Disclosure of timing of required repayments, sinking fund requirements, and other redeemable securities at fixed or determinable prices and dates in the five years immediately following the date of the latest balance sheet presented in the financial statements, and the amount thereafter to fully repay the principal of long-term debt. These disclosures may be made either on an individual debt or security basis, by type of debt or security basis, or on a combined basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 3

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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-Number 210

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Weighted average interest rate of long-term debt outstanding.

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