Shareholders' Equity - Additional Information (Detail) $ in Thousands		3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) shares	Jun. 30, 2017 USD ($) shares	Jun. 30, 2018 shares	Jun. 30, 2017 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares
Class of Stock [Line Items]
Preferred stock, redemption date			Jun. 30, 2017
Series B Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock shares outstanding converted into common stock	130
Each share of preferred stock converted into common stock	2.78
Preferred shares converted into common stock, shares	361	361		361
Preferred stock, shares outstanding			0		0
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares outstanding			0		0	550
Payment for redemption of preferred stock | $	$ 10	$ 10		$ 10
Amount recorded in excess of carrying value over redemption value | $		$ 459		$ 459	$ 500