Accounts Receivable (Details) (USD $) In Thousands	Sep. 30, 2011	Mar. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 145,155	$ 184,040
Less allowance for doubtful accounts	2,746	2,838
Accounts receivable, net	142,409	181,202
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	143,633	181,840
Other Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 1,522	$ 2,200