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Segment information - Additional Information (Detail) - segment
3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Segment Reporting Information [Line Items]        
Number of reportable segments 2 1    
Number of operating segments 2 1    
Maximum | Sales Revenue, Net | Outside of the United States        
Segment Reporting Information [Line Items]        
Concentration risk     10.00% 10.00%