Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Related Party Transaction [Line Items]
Accounts receivable	$ 32,316	$ 61,981
Accounts payable	37,520	38,937
Purchases	210,113	157,851	140,432
Zimbabwe subsidiary [Member]
Related Party Transaction [Line Items]
Accounts receivable		$ 38,380