Investments - Summarized Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current	$ 0
Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		$ 26,597,000
Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		17,702,000
Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		8,895,000
Recurring [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	10,943,000	17,702,000
Recurring [Member] | Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	$ 10,943,000	17,702,000
Recurring [Member] | FDIC Guaranteed Certificates of Deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		1,920,000
Recurring [Member] | FDIC Guaranteed Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		1,920,000
Recurring [Member] | Corporate Notes/Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		6,975,000
Recurring [Member] | Corporate Notes/Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sales securities - current		$ 6,975,000