Asset and Liabilities Carried at Fair Value Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 205,731
Short term investments	97,891
Contingent consideration, short-term	8,042	7,293
Contingent consideration, long-term	16,909	12,896
Fair Value, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	205,731
Short term investments	97,891
Fair Value, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, short-term	8,042
Contingent consideration, long-term	$ 16,909