Reconciliation of Changes in Fair Value of Level Three Financial Assets (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2012
Auction Rate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
ARSs redeemed by issuers at par	$ 19,300
Fair Value, Measurements, Recurring | Auction Rate Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	1,461
Change in fair value (included within research and development expense)	0
ARSs redeemed by issuers at par	(1,650)
Unrealized gains included in accumulated other comprehensive income (loss)	190
Unrealized gain (loss) included in earnings	(1)
Payments	0
Balance at end of period	0
Fair Value, Measurements, Recurring | Contingent Purchase Consideration
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(8,213)
Change in fair value (included within research and development expense)	(346)
ARSs redeemed by issuers at par	0
Unrealized gains included in accumulated other comprehensive income (loss)	0
Unrealized gain (loss) included in earnings	0
Payments	1,516
Balance at end of period	(7,043)
Fair Value, Measurements, Recurring | Contingent Contractual Non-Compliance Liability
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(700)
Change in fair value (included within research and development expense)	135
ARSs redeemed by issuers at par	0
Unrealized gains included in accumulated other comprehensive income (loss)	0
Unrealized gain (loss) included in earnings	0
Payments	0
Balance at end of period	$ (565)