Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Short-term investments:
Total short-term investments	$ 18,888	$ 13,280
Restricted cash equivalents—money market fund		250
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	3,296	9,173
Short-term investments:
Total short-term investments	18,888	13,280
Restricted cash equivalents—money market fund		250
Total assets measured at fair value	22,184	22,703
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	11,465	6,245
Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	500	1,500
Short-term investments:
Total short-term investments	11,465	6,245
Corporate debt [Member]
Short-term investments:
Total short-term investments	7,423	6,028
Corporate debt [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	7,423	6,028
Treasury bonds [Member]
Short-term investments:
Total short-term investments		1,007
Treasury bonds [Member] | Recurring basis [Member]
Short-term investments:
Total short-term investments		1,007
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	2,796	5,404
Short-term investments:
Restricted cash equivalents—money market fund		250
Total assets measured at fair value	2,796	5,654
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	500	3,769
Short-term investments:
Total short-term investments	18,888	13,280
Total assets measured at fair value	19,388	17,049
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	500	1,500
Short-term investments:
Total short-term investments	11,465	6,245
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate debt [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	7,423	6,028
Direct or Indirect Observable Inputs (Level 2) [Member] | Treasury bonds [Member] | Recurring basis [Member]
Short-term investments:
Total short-term investments		1,007
Money market funds [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	2,796	5,404
Money market funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	$ 2,796	$ 5,404