Investments (Tables)

9 Months Ended

Dec. 31, 2014

Investments [Abstract]

Summary of available-for-sale securities

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

	Available-for-sale Securities
	Adjusted Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Government agency bonds	$	736,615	$	113	$	(1,866	)	$	734,862
Municipal bonds	45,140		74		(32		)	45,182
Auction rate securities	9,825		—		—			9,825
Time deposits (1)	8,699		—		—			8,699
Corporate bonds and debt	938,331		927		(1,397		)	937,861
Marketable equity securities	3,600		33,314		—			36,914
	$	1,742,210	$	34,428	$	(3,295	)	$	1,773,343

(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 available-for-sale securities in a continuous unrealized loss position

The following tables show all investments in an unrealized loss position for which an other-than-temporary impairment has not been recognized and the related gross unrealized losses and fair value, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position (amounts in thousands):

	December 31, 2014
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Government agency bonds	$	568,466	$	(1,561	)	$	64,695	$	(305	)	$	633,161	$	(1,866	)
Municipal bonds	13,533		(32		)	—		—			13,533		(32		)
Corporate bonds and debt	460,372		(1,363		)	5,988		(34		)	466,360		(1,397		)
	$	1,042,371	$	(2,956	)	$	70,683	$	(339	)	$	1,113,054	$	(3,295	)

	March 31, 2014
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Government agency bonds	$	522,159	$	(3,172	)	$	—	$	—		$	522,159	$	(3,172	)
Municipal bonds	2,625		(13		)	1,196		(1		)	3,821		(14		)
Corporate bonds and debt	256,717		(804		)	—		—			256,717		(804		)
	$	781,501	$	(3,989	)	$	1,196	$	(1	)	$	782,697	$	(3,990	)

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 December 31, 2014, by contractual maturity, excluding marketable equity securities of $36.9 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	$	216,444	$	258	$	(9	)	$	216,693
Due after one year and through five years	1,428,901		835		(3,081		)	1,426,655
Due after five years and through ten years	77,250		21		(205		)	77,066
Due after ten years	9,825		—		—			9,825
	$	1,732,420	$	1,114	$	(3,295	)	$	1,730,239