Capital Stock - Additional Information (Detail) - shares	Mar. 31, 2018	Dec. 31, 2017
Class Of Stock Disclosures [Abstract]
Authorized capital stock	485,000,000	485,000,000
Common stock, shares authorized	475,000,000	475,000,000
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0