Fair Value Measurement - Summary of Fair Value Measurements of Cash Equivalents, Available-for-Sale Securities and Contingent Consideration Liability (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 227,461	$ 128,224
Total contingent consideration liabilities	1,700	1,570
Cash equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	7,193	6,934
Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	220,268
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	7,193	6,934
Level 1 [Member] | Cash equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	7,193	6,934
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	220,268	121,290
Level 2 [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	220,268
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total contingent consideration liabilities	1,700	1,570
Money market funds [Member] | Cash equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	7,193	6,934
Money market funds [Member] | Level 1 [Member] | Cash equivalents [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	7,193	6,934
Commercial paper securities [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	36,247
Commercial paper securities [Member] | Level 2 [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	36,247
Corporate debt securities [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	20,611
Corporate debt securities [Member] | Level 2 [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	20,611
U.S. government sponsored entity debt securities [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	163,410	121,290
U.S. government sponsored entity debt securities [Member] | Level 2 [Member] | Marketable securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	163,410	121,290
Contingent consideration liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total contingent consideration liabilities	1,700	1,570
Contingent consideration liability [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total contingent consideration liabilities	$ 1,700	$ 1,570