Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Short-term investments:
Total short-term investments	$ 13,280	$ 13,263
Restricted cash equivalents—money market fund	250	250
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	9,173	10,364
Short-term investments:
Total short-term investments	13,280	13,263
Restricted cash equivalents—money market fund	250	250
Total assets measured at fair value	22,703	23,877
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	5,404	9,362
Short-term investments:
Restricted cash equivalents—money market fund	250	250
Total assets measured at fair value	5,654	9,612
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	3,769	1,002
Short-term investments:
Total short-term investments	13,280	13,263
Total assets measured at fair value	17,049	14,265
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	6,245	550
Corporate commercial paper [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	1,500
Short-term investments:
Total short-term investments	6,245	550
Corporate commercial paper [Member] | Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	1,500
Short-term investments:
Total short-term investments	6,245	550
Corporate debt [Member]
Short-term investments:
Total short-term investments	6,028	12,713
Corporate debt [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	2,269	1,002
Short-term investments:
Total short-term investments	6,028	12,713
Corporate debt [Member] | Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	2,269	1,002
Short-term investments:
Total short-term investments	6,028	12,713
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
Treasury bonds [Member] | Direct or Indirect Observable Inputs (Level 2) [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	5,404	9,362
Money market funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	$ 5,404	$ 9,362