Segmented information - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 business_unit country
Segment Reporting [Abstract]
Number of business units \| business_unit	2
Number of countries in which entity operates \| country	2

The number of countries in which the entity operates as of balance sheet date.

No definition available.

Name:	us-gaap_NumberOfCountriesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant