Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest income	$ 809,559.0	$ 296,007.0
Gross realized gain (loss)	0	0
Long-term debt, fair value	299,000,000		$ 327,600,000
Income tax effects deferred from past intercompany transactions	$ 0	$ 46,000
Warrants exercise price (in dollars per share)	$ 0.05
Long-term Receivable | Accounting Standards Update 2016-16, Income Tax Effect Deferred From Past Intercompany Transactions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax effects deferred from past intercompany transactions			$ 2,100,000