Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Stock-Based Compensation - Assumptions Used for Restricted Stock Grants (Detail)

v3.19.1
Stock-Based Compensation - Assumptions Used for Restricted Stock Grants (Detail) - Restricted Stock Units (Market Condition) [Member] - $ / shares
12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
August 2017 Grant    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield (per annum)   3.00%
Expected volatility   30.10%
Risk free interest rate   1.50%
Expected life in years   3 years 3 months 19 days
JHX stock price at grant date (A$ per share))   $ 17.91
Number of restricted stock units (in shares)   932,393
September 2018 Grant    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield (per annum) 3.00%  
Expected volatility 26.80%  
Risk free interest rate 2.70%  
Expected life in years 2 years 10 months 25 days  
JHX stock price at grant date (A$ per share)) $ 20.87  
Number of restricted stock units (in shares) 49,381  
August 2018 Grant    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield (per annum) 3.00%  
Expected volatility 28.10%  
Risk free interest rate 2.70%  
Expected life in years 3 years  
JHX stock price at grant date (A$ per share)) $ 22  
Number of restricted stock units (in shares) 663,738