Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Short-term investments:
Total short-term investments	$ 6,131	$ 7,295
Restricted cash-money market fund	250	250
Corporate debt securities [Member]
Short-term investments:
Total short-term investments	4,881	4,794
Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	1,250	1,500
Foreign government bonds [Member]
Short-term investments:
Total short-term investments		1,001
Recurring basis [Member]
Cash equivalents:
Total cash equivalents	14,337	10,989
Short-term investments:
Total short-term investments	6,131	7,295
Restricted cash-money market fund	250	250
Total assets measured at fair value	20,718	18,534
Recurring basis [Member] | Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	652	2,000
Short-term investments:
Total short-term investments	4,881	4,794
Recurring basis [Member] | Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	1,250	1,500
Recurring basis [Member] | Foreign government bonds [Member]
Short-term investments:
Total short-term investments		1,001
Recurring basis [Member] | Money market funds [Member]
Cash equivalents:
Total cash equivalents	12,435	8,989
Recurring basis [Member] | Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	1,250
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	12,435	8,989
Short-term investments:
Total short-term investments
Restricted cash-money market fund	250	250
Total assets measured at fair value	12,685	9,239
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member] | Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents
Short-term investments:
Total short-term investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member] | Corporate commercial paper [Member]
Short-term investments:
Total short-term investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member] | Foreign government bonds [Member]
Short-term investments:
Total short-term investments
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member] | Money market funds [Member]
Cash equivalents:
Total cash equivalents	12,435	8,989
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring basis [Member] | Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member]
Cash equivalents:
Total cash equivalents	1,902	2,000
Short-term investments:
Total short-term investments	6,131	7,295
Restricted cash-money market fund
Total assets measured at fair value	8,033	9,295
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member] | Corporate debt securities [Member]
Cash equivalents:
Total cash equivalents	652	2,000
Short-term investments:
Total short-term investments	4,881	4,794
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member] | Corporate commercial paper [Member]
Short-term investments:
Total short-term investments	1,250	1,500
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member] | Foreign government bonds [Member]
Short-term investments:
Total short-term investments		1,001
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member] | Money market funds [Member]
Cash equivalents:
Total cash equivalents
Direct or Indirect Observable Inputs (Level 2) [Member] | Recurring basis [Member] | Corporate commercial paper [Member]
Cash equivalents:
Total cash equivalents	$ 1,250