Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Short-term investments:
Total short-term investments	$ 21,280	$ 18,888
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	964	3,296
Short-term investments:
Total short-term investments	21,280	18,888
Total assets measured at fair value	22,244	22,184
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	10,149	11,465
Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		500
Short-term investments:
Total short-term investments	10,149	11,465
Corporate debt securities [Member]
Short-term investments:
Total short-term investments	11,131	7,423
Corporate debt securities [Member] | Recurring basis [Member]
Short-term investments:
Total short-term investments	11,131	7,423
Money market funds [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	964	2,796
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	964	2,796
Short-term investments:
Total assets measured at fair value	964	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	964	2,796
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		500
Short-term investments:
Total short-term investments	21,280	18,888
Total assets measured at fair value	21,280	19,388
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		500
Short-term investments:
Total short-term investments	10,149	11,465
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate debt securities [Member] | Recurring basis [Member]
Short-term investments:
Total short-term investments	$ 11,131	$ 7,423