Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Accounting Policies [Abstract]
Unrealized gain (loss) on available-for-sale investments	$ (3,000)	$ 9,000	$ 166,000	$ 75,000
Realized investment gains or losses	0	$ 0	0	$ 0
Investments owned, at fair value			0
Long-term debt, fair value	$ 211,300,000		$ 211,300,000		$ 140,100,000
Warrants exercise price (in USD per share)	$ 0.05		$ 0.05