Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 262,944	$ 182,530
Short-term investments	468	576
Contingent consideration	(9,657)	(9,571)
Deferred compensation	(2,091)	(2,073)
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	262,944	181,198
Short-term investments	0	0
Contingent consideration	0	0
Deferred compensation	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	1,332
Short-term investments	468	576
Contingent consideration	0	0
Deferred compensation	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Contingent consideration	(9,657)	(9,571)
Deferred compensation	$ (2,091)	$ (2,073)