Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Short-term investments:
Total short-term investments	$ 17,828	$ 18,888
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	4,429	3,296
Short-term investments:
Total short-term investments	17,828	18,888
Total assets measured at fair value	22,257	22,184
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	10,895	11,465
Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	3,498	500
Short-term investments:
Total short-term investments	10,895	11,465
Corporate debt securities [Member]
Short-term investments:
Total short-term investments	6,933	7,423
Corporate debt securities [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	750
Short-term investments:
Total short-term investments	6,933	7,423
Money market funds [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	181	2,796
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	181	2,796
Short-term investments:
Total assets measured at fair value	181	2,796
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	181	2,796
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	4,248	500
Short-term investments:
Total short-term investments	17,828	18,888
Total assets measured at fair value	22,076	19,388
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	3,498	500
Short-term investments:
Total short-term investments	10,895	11,465
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate debt securities [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	750
Short-term investments:
Total short-term investments	$ 6,933	$ 7,423