Fair Value Hierarchy of Financial Assets Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents (money market accounts and commercial paper investments)	77,935	325,652
Fair Value Assets And Liabilities Measured On Recurring Basis, Total	77,935	325,652
Acquisition Contingent Consideration Obligations	3,320
Fair Value Assets And Liabilities Measured On Recurring Basis, Total	3,320
Cash Equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique (Approach)	Market	Market
Acquisition Contingent Consideration Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique (Approach)	Income
Fair Value, Inputs, Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents (money market accounts and commercial paper investments)	77,935	325,652
Fair Value Assets And Liabilities Measured On Recurring Basis, Total	77,935	325,652
Fair Value, Inputs, Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Acquisition Contingent Consideration Obligations	3,320
Fair Value Assets And Liabilities Measured On Recurring Basis, Total	3,320