Fair Value Measurements - Summary of Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Short-term investments:
Short-term investments	$ 79,508	$ 86,529
U.S. Government Securities [Member]
Short-term investments:
Short-term investments	6,977	15,965
Asset Backed Securities [Member]
Short-term investments:
Short-term investments	6,238	8,588
Corporate Securities [Member]
Short-term investments:
Short-term investments	36,077	19,954
Commercial Paper [Member]
Short-term investments:
Short-term investments	30,216	42,022
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Money Market Funds [Member]
Cash equivalents:
Cash equivalents	20,193	14,710
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Government Securities [Member]
Short-term investments:
Short-term investments	6,977	15,965
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Foreign exchange derivatives not designated as hedging instruments	85	26
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset Backed Securities [Member]
Short-term investments:
Short-term investments	6,238	8,588
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member]
Cash equivalents:
Cash equivalents		2,371
Short-term investments:
Short-term investments	36,077	19,954
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
Cash equivalents:
Cash equivalents		4,411
Short-term investments:
Short-term investments	30,216	42,022
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Contingent consideration	$ 12,347	$ 12,214