Fair Value of Financial Instruments - Summary of Cash, Cash Equivalents and Short-Term Investments, Available-for-Sale, by Type of Instrument (Detail) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Dec. 31, 2014 |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents | $ 16,424 | $ 34,809 | [1] | $ 19,313 | $ 13,403 |
Cash and cash equivalents and short-term investments, available-for-sale | 108,683 | 124,300 | | | |
Fair Value on Recurring Basis [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents | 16,424 | 34,809 | | | |
Short-term investments, available-for-sale | 92,259 | 89,491 | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 108,683 | 124,300 | | | |
Fair Value on Recurring Basis [Member] | Cash [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 5,863 | 2,702 | | | |
Fair Value on Recurring Basis [Member] | Money Market Funds [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 10,561 | 26,856 | | | |
Fair Value on Recurring Basis [Member] | Corporate Debt Securities [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 41,298 | 57,517 | | | |
Fair Value on Recurring Basis [Member] | Commercial Paper [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 50,961 | 37,225 | | | |
Level 1 [Member] | Fair Value on Recurring Basis [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 16,424 | 29,558 | | | |
Level 1 [Member] | Fair Value on Recurring Basis [Member] | Cash [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 5,863 | 2,702 | | | |
Level 1 [Member] | Fair Value on Recurring Basis [Member] | Money Market Funds [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 10,561 | 26,856 | | | |
Level 2 [Member] | Fair Value on Recurring Basis [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 92,259 | 94,742 | | | |
Level 2 [Member] | Fair Value on Recurring Basis [Member] | Corporate Debt Securities [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | 41,298 | 57,517 | | | |
Level 2 [Member] | Fair Value on Recurring Basis [Member] | Commercial Paper [Member] | | | | | |
Net Investment [Line Items] | | | | | |
Cash and cash equivalents and short-term investments, available-for-sale | $ 50,961 | $ 37,225 | | | |
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[1] | Amounts have been derived from the December 31, 2015 audited financial statements included in the Company's Annual Report on Form 10-K filed with the Securities and Exchange Commission. |