Fair Value Measurement - Summary of Fair Value Measurements of Cash Equivalents, and Available-for-Sale Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 10,704	$ 65,937
Total marketable securities	159,321	139,518
Total cash equivalents and marketable securities	170,025	205,455
Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	10,704	25,070
Commercial paper securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents		2,000
Total marketable securities	32,473	30,717
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	10,704	65,937
Total cash equivalents and marketable securities	10,704	65,937
Level 1 [Member] | Money market funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	10,704	25,070
Level 1 [Member] | Commercial paper securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents		2,000
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	159,321	139,518
Total cash equivalents and marketable securities	159,321	139,518
Level 2 [Member] | Commercial paper securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	32,473	30,717
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	11,766	17,263
Corporate debt securities [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	11,766	17,263
U.S. government sponsored entity debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents		38,867
Total marketable securities	115,082	91,538
U.S. government sponsored entity debt securities [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents		38,867
U.S. government sponsored entity debt securities [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total marketable securities	$ 115,082	$ 91,538