Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Short-term investments:
Total short-term investments	$ 16,279	$ 13,280
Restricted cash equivalents—money market fund	250	250
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	2,036	9,173
Short-term investments:
Total short-term investments	16,279	13,280
Restricted cash equivalents—money market fund	250	250
Total assets measured at fair value	18,565	22,703
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	10,990	6,245
Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	500	1,500
Short-term investments:
Total short-term investments	10,990	6,245
Corporate debt securities [Member]
Short-term investments:
Total short-term investments	5,289	6,028
Corporate debt securities [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	5,289	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	1,536	5,404
Short-term investments:
Restricted cash equivalents—money market fund	250	250
Total assets measured at fair value	1,786	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	16,279	13,280
Total assets measured at fair value	16,779	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	10,990	6,245
Direct or Indirect Observable Inputs (Level 2) [Member] | Corporate debt securities [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents		2,269
Short-term investments:
Total short-term investments	5,289	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	1,536	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	$ 1,536	$ 5,404