Marketable Securities (Summary of available-for-sale securities ) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Securities in a continuous loss position for less than 12 months	$ 0
Securities in a continuous loss position for more than 12 months	1,048
Aggregate fair value	1,048
Securities in a continuous loss position for less than 12 months	0
Securities in a continuous loss position for more than 12 months	62
Unrealized losses	62
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost	22,153	23,183
Gross Unrealized Gains	2,538	2,249
Gross Unrealized Losses	62	39
Estimated fair value	$ 24,629	$ 25,393

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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