Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Minimum Maturity Period Of Investments To Be Classified As Available For Sale Securities	90 days
Gross unrealized losses	$ 22	$ 39
Amortized costs	82,350	118,783
Sixteen Different Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses	22
Amortized costs	31,100
Number of securities	16
37 Different Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		39
Amortized costs		$ 72,600
Number of securities		37