Summary of Cash Equivalents and Marketable Securities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 7,501,000	$ 0
Fair Value Measurements Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	16,274,000	36,611,000
Marketable securities	7,501,000
Cash Equivalents, and Marketable Securities Fair Value Disclosure, Total	23,775,000
Fair Value Measurements Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	11,462,000	28,777,000
Cash Equivalents, and Marketable Securities Fair Value Disclosure, Total	11,462,000
Fair Value Measurements Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,812,000	$ 7,834,000
Marketable securities	7,501,000
Cash Equivalents, and Marketable Securities Fair Value Disclosure, Total	$ 12,313,000