Anti-dilutive Security not Included In Diluted per Share Calculations (Parenthetical) (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	0		3,680
Conversion of preferred stock to common stock	1,083,938	3,311,482
Series A Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Preferred stock, shares outstanding	0	5,500
Conversion of preferred stock to common stock		1,100,000