Investments (Tables)

6 Months Ended

Sep. 30, 2014

Investments [Abstract]

Summary of available-for-sale securities

The following is a summary of available-for-sale securities at September 30, 2014 (amounts in thousands):

	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	668,639	$	129	$	(2,560	)	$	666,208
Municipal bonds	41,097		66		(2		)	41,161
Auction rate securities	9,825		—		—			9,825
Time deposits (1)	20,160		—		—			20,160
Corporate bonds and debt	904,243		2,150		(800		)	905,593
	$	1,643,964	$	2,345	$	(3,362	)	$	1,642,947

(1) Time deposits in various financial institutions with maturities greater than three months that will mature within one year.

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

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 September 30, 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	$	250,615	$	742	$	(5	)	$	251,352
Due after one year and through five years	1,264,898		1,552		(2,227		)	1,264,223
Due after five years and through ten years	112,436		51		(1,130		)	111,357
Due after ten years	9,825		—		—			9,825
	$	1,637,774	$	2,345	$	(3,362	)	$	1,636,757