Fair Value of Financial Instruments - Summary of Fair Value Hierarchy for Financial Assets (Detail) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | $ 62,829 | |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 62,829 | $ 66,676 |
Fair Value, Measurements, Recurring [Member] | Money Market Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 1,082 | 2,197 |
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 50,997 | 49,834 |
Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 5,006 | 10,715 |
Fair Value, Measurements, Recurring [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 2,000 | 1,996 |
Fair Value, Measurements, Recurring [Member] | Corporate Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 3,744 | 1,934 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 1,082 | 2,197 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 1,082 | 2,197 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 61,747 | 64,479 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 50,997 | 49,834 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 5,006 | 10,715 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 2,000 | 1,996 |
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 3,744 | 1,934 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Securities [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Federal Agency Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasuries [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | 0 | 0 |
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Notes [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total | $ 0 | $ 0 |