Schedule of Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 135,025	$ 117,255
Marketable securities	104,207	96,261
Derivative financial instruments, assets	8	150
Total assets	239,240	213,666
Contingent purchase consideration	(7,043)	(8,213)
Contingent contractual non-compliance liability	(565)	(700)
Derivative financial instruments, liabilities	(287)	(166)
Total liabilities	(7,895)	(9,079)
U.S. Government And Municipal Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	54,871	31,635
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	32,361	22,469
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	3,213	3,207
Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13,762	19,877
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		19,073
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	135,025	117,255
Derivative financial instruments, assets	0	0
Total assets	203,658	168,767
Contingent purchase consideration	0	0
Contingent contractual non-compliance liability	0	0
Derivative financial instruments, liabilities	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 1 | U.S. Government And Municipal Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	54,871	31,635
Fair Value, Inputs, Level 1 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 1 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 1 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13,762	19,877
Fair Value, Inputs, Level 1 | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Derivative financial instruments, assets	8	150
Total assets	35,582	43,438
Contingent purchase consideration	0	0
Contingent contractual non-compliance liability	0	0
Derivative financial instruments, liabilities	(287)	(166)
Total liabilities	(287)	(166)
Fair Value, Inputs, Level 2 | U.S. Government And Municipal Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 2 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	32,361	22,469
Fair Value, Inputs, Level 2 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	3,213	3,207
Fair Value, Inputs, Level 2 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 2 | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		17,612
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Derivative financial instruments, assets	0	0
Total assets	0	1,461
Contingent purchase consideration	(7,043)	(8,213)
Contingent contractual non-compliance liability	(565)	(700)
Derivative financial instruments, liabilities	0	0
Total liabilities	(7,608)	(8,913)
Fair Value, Inputs, Level 3 | U.S. Government And Municipal Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 3 | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 3 | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 3 | Corporate Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Fair Value, Inputs, Level 3 | Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		$ 1,461