Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross realized gain (loss)	$ 0	$ 0	$ 0	$ 0
Investments owned, at fair value			0
Long-term debt, fair value	$ 269,800,000		$ 269,800,000		$ 209,600,000
Warrants exercise price (in dollars per share)	$ 0.05		$ 0.05
Accounting Standards Update 2016-16, Income Tax Effects Recorded As Other Assets | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax effects from past intercompany transactions	$ 2,300,000		$ 2,300,000