Marketable Equity Investments - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Apr. 30, 2015	Sep. 30, 2017
Investment [Line Items]
Carrying value of investment		$ 0
Gain on sale of investment in marketable equity securities		3,466,000
Aduro
Investment [Line Items]
Preferred shares converted to common stock	396,700
Gain on sale of investment in marketable equity securities		$ 3,500,000
Common stock, shares outstanding		0