Investable Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value	$ 19,487	$ 31,487
US Government-sponsored Enterprises Debt Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value	74,459	24,176
US Government-sponsored Enterprises Debt Securities \| Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value	17,982	41,761
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	111,962	97,440
Gross Unrealized Gains	7	14
Gross Unrealized Losses	(41)	(30)
Fair Market Value	111,928	97,424
Level 2 \| US Treasury Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	19,487	31,487
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	19,487	31,487
Level 2 \| US Government-sponsored Enterprises Debt Securities \| Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	74,478	24,174
Gross Unrealized Gains	5	6
Gross Unrealized Losses	(24)	(4)
Fair Market Value	74,459	24,176
Level 2 \| US Government-sponsored Enterprises Debt Securities \| Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	17,997	41,779
Gross Unrealized Gains	2	8
Gross Unrealized Losses	(17)	(26)
Fair Market Value	$ 17,982	$ 41,761

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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