Investments (Tables)

12 Months Ended

Mar. 31, 2014

Investments [Abstract]

Summary of available-for-sale securities

The following is a summary of available-for-sale securities at March 31, 2014 (amounts in thousands):

	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	684,451	$	114	$	(3,171	)	$	681,394
Municipal bonds	41,622		101		(14		)	41,709
Auction rate securities	9,825		—		—			9,825
Corporate bonds and debt	941,524		3,247		(805		)	943,966
	$	1,677,422	$	3,462	$	(3,990	)	$	1,676,894

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

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, 2014, by contractual maturity, excluding corporate debt of $6.2 million, which has 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	$	210,129	$	1,234	$	—		$	211,363
Due after one year and through five years	1,308,844		2,228		(1,958		)	1,309,114
Due after five years and through ten years	142,434		—		(2,032		)	140,402
Due after ten years	9,825		—		—			9,825
	$	1,671,232	$	3,462	$	(3,990	)	$	1,670,704

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). 

	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