Marketable securities (Tables)

12 Months Ended

Mar. 31, 2012

Marketable securities [Abstract]

Available-for-sale debt securities

Available-for-sale debt securities consist of the following:

	March 31, 2012
(In thousands)	Estimated fair value		Gains in accumulated other comprehensive income		Losses in accumulated other comprehensive income
Current:
Municipal bonds and notes	$	33,723	$	52
Government agency bonds		92,829		123
Commercial paper		239,393		334	$	( 70	)
Certificates of deposit		91,819		320
Corporate bonds		210,852		76		( 79	)
Floating rate notes		178,939		281		( 22	)
Total current securities		847,555		1,186		( 171	)
Noncurrent:
Municipal bonds and notes		35,890		45
Government agency bonds		60,087		185
Commercial paper		14,682		111
Corporate bonds		305,697		779		( 82	)
Auction rate notes		25,089
Floating rate notes		254,193				( 10,547	)
Total non-current securities		695,638		1,120		( 10,629	)
Total available-for-sale debt securities	$	1,543,193	$	2,306	$	(10,800	)

	March 31, 2011
(In thousands)	Estimated fair value		Gains in accumulated other comprehensive income		Losses in accumulated other comprehensive income
Current:
Variable rate demand notes	$	178,435
Municipal bonds and notes		144,950	$	195
Government agency bonds		160,894		207
Commercial paper		606,986		753	$	( 107	)
Certificates of deposit		241,964		73
Corporate bonds		252,146		289		( 71	)
Floating rate notes		127,928				( 11,582	)
Total current securities		1,713,303		1,517		( 11,760	)
Noncurrent:
Municipal bonds and notes		13,534		21
Government agency bonds		54,598		4,504		( 122	)
Certificates of deposit		9,436				( 1	)
Corporate bonds		266,366				( 2,401	)
Auction rate notes		34,539				( 1,906	)
Floating rate notes		122,319		391		( 2,782	)
Total non-current securities		500,792		4,916		( 7,212	)
Total available-for-sale debt securities	$	2,214,095	$	6,433	$	(18,972	)

Contractual maturities of available-for-sale debt securities

Contractual maturities of available-for-sale debt securities at March 31, 2012, are as follows:

(In thousands)

	Estimated fair value
Within one year	$	847,555
1-5 years		659,786
5-10 years		15,196
After 10 years		20,656
	$	1,543,193