Net Loss Per Common Share - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Amounts allocated to participating securities	$ 0	$ 0
Participating securities outstanding, shares	0	0
Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	4.50%