Fair Value Measurements (Tables)

6 Months Ended

Sep. 30, 2012

Fair Value Measurements [Abstract]

Schedule of Assets Measured at Fair Value of Debt Securities

	Fair Value Measurements Using
	Level 1			Level 2			Level 3			Total
	(In thousands)
September 30, 2012
Cash and cash equivalents		$	103,045		$	420		$	—		$	103,465
Marketable securities:
U.S. government and agency securities			130,138			—			—			130,138
Corporate debt obligations			—			168,590			—			168,590
Mortgage-backed securities			—			52,130			—			52,130
Municipal bonds			—			30,093			—			30,093
			130,138			250,813			—			380,951
		$	233,183		$	251,233		$	—		$	484,416
April 1, 2012
Cash and cash equivalents		$	162,266		$	2,250		$	—		$	164,516
Marketable securities:
U.S. government and agency securities			141,859			—			—			141,859
Corporate debt obligations			—			167,668			—			167,668
Asset and mortgage-backed securities			—			46,594			—			46,594
Municipal bonds			—			16,568			—			16,568
Other debt securities			—			750			—			750
			141,859			231,580			—			373,439
		$	304,125		$	233,830		$	—		$	537,955