Cash And Cash Equivalents And Investments (Schedule Of Investments By Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Cash and Cash Equivalents and Investments [Abstract]
Trading securities, due in one year or less	$ 8,616	$ 8,650
Due in 12 months or less	58,873	62,504
Due in 12 months to 24 months	27,394	29,903
Due in 24 months to 36 months	15,033	2,682
Due in 36 months to 49 months	24,342	7,398
Short-term investments	134,258	111,137
Available for sale securities, due after ten years	13,600	25,900
Long-term investments	$ 13,600	$ 25,900