Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 233,679	$ 172,803
Less allowance for doubtful accounts	3,222	2,602
Accounts receivable, net	230,457	170,201
Trade Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	230,203	171,274
Other Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivable amounts	$ 3,476	$ 1,529