Capital Stock - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Class of Stock [Line Items]
Authorized capital stock	300,000,000
Common stock, par value | $ / shares	$ 0.01
Preferred stock, par value | $ / shares	$ 0.01
Authorized preferred stock	15,000,000
Directors [Member]
Class of Stock [Line Items]
Common stock issued due to stock option exercises	3,706
Common Stock [Member]
Class of Stock [Line Items]
Common stock issued due to stock option exercises	90,420