Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Apr. 01, 2012
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Fair Value Less than 12 months	$ 6,508	$ 120,819
Unrealized Loss Less than 12 months	(1)	(33)
Fair Value 12 months or Greater	0	0
Unrealized Loss 12 months or Greater	0	0
Fair Value Total	6,508	120,819
Unrealized Loss Total	(1)	(33)
Corporate bonds [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Fair Value Less than 12 months	552	4,213
Unrealized Loss Less than 12 months	(1)	(7)
Fair Value 12 months or Greater	0	0
Unrealized Loss 12 months or Greater	0	0
Fair Value Total	552	4,213
Unrealized Loss Total	(1)	(7)
U.S. government treasuries and agencies securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Fair Value Less than 12 months	1,350	114,056
Unrealized Loss Less than 12 months	0	(24)
Fair Value 12 months or Greater	0	0
Unrealized Loss 12 months or Greater	0	0
Fair Value Total	1,350	114,056
Unrealized Loss Total	0	(24)
International government bonds [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Fair Value Less than 12 months	4,606	2,550
Unrealized Loss Less than 12 months	0	(2)
Fair Value Total	4,606	2,550
Unrealized Loss Total	$ 0	$ (2)