Investments (Tables)

12 Months Ended

Mar. 31, 2013

Investments [Abstract]

Summary of available-for-sale securities

The following is a summary of available-for-sale securities at March 31, 2013 (amounts in thousands):

	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	558,116	$	335	$	(298	)	$	558,153
Municipal bonds	25,000		146		(8		)	25,138
Auction rate securities	33,459		332		—			33,791
Corporate bonds and debt	680,144		5,137		(159		)	685,122
Marketable equity securities	5,270		239		—			5,509
	$	1,301,989	$	6,189	$	(465	)	$	1,307,713

The following is a summary of available-for-sale securities at March 31, 2012 (amounts in thousands):

	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	342,025	$	476	$	(397	)	$	342,104
Municipal bonds	19,888		234		—			20,122
Auction rate securities	10,246		—		—			10,246
Corporate bonds and debt	770,891		4,150		(937		)	774,104
Marketable equity securities	5,864		188		(788		)	5,264
	$	1,148,914	$	5,048	$	(2,122	)	$	1,151,840

Summary of amortized cost and estimated fair value of available-for-sale securities, by maturity

The amortized cost and estimated fair value of the available-for-sale securities at March 31, 2013, by maturity, excluding marketable equity securities of $5.5 million and corporate debt of $6.2 million, which have no contractual maturity, are shown below (amounts in thousands).  Expected maturities can differ from contractual maturities because the issuers of the securities may have the right to prepay obligations without prepayment penalties, and the Company views its available-for-sale securities as available for current operations.

	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale
Due in one year or less	$	350,349	$	1,933	$	(3	)	$	352,279
Due after one year and through five years	795,952		3,666		(212		)	799,406
Due after five years and through ten years	115,901		116		(250		)	115,767
Due after ten years	28,327		235		—			28,562
	$	1,290,529	$	5,950	$	(465	)	$	1,296,014

The amortized cost and estimated fair value of the available-for-sale securities at March 31, 2012, by maturity, excluding marketable equity securities of $5.3 million and corporate debt of $4.6 million, which have no contractual maturity, are shown below (amounts in thousands). 

	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale
Due in one year or less	$	268,501	$	1,537	$	(21	)	$	270,017
Due after one year and through five years	839,677		3,323		(1,297		)	841,703
Due after five years and through ten years	25,177		—		(16		)	25,161
Due after ten years	5,069		—		—			5,069
	$	1,138,424	$	4,860	$	(1,334	)	$	1,141,950