Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Mar. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 151,948	$ 184,040
Less allowance for doubtful accounts	2,671	2,838
Accounts receivable, net	149,277	181,202
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	150,295	181,840
Other Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 1,653	$ 2,200