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Equity Based Compensation (Narrative) (Detail)
6 Months Ended 12 Months Ended
Sep. 30, 2019
USD ($)
Item
shares
Mar. 31, 2019
USD ($)
Mar. 31, 2018
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense | $   $ 9,807  
Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares reserved for future issuance 25,000,000    
Omnibus Incentive Plan [Member] | Joint Venture [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense | $ $ 6,096,000    
Unrecognized compensation expense | $ $ 87,211,000    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted in period     316,000
Restricted Stock Units (RSUs) [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted in period 4,436,758    
Restricted Stock Units (RSUs) [Member] | Omnibus Incentive Plan [Member] | Graded Vesting Schedule [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years    
Restricted Stock Units (RSUs) [Member] | Omnibus Incentive Plan [Member] | Share-based Payment Arrangement, Tranche One [Member] | Cliff Vesting Schedule [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Restricted Stock Units (RSUs) [Member] | Omnibus Incentive Plan [Member] | Share-based Payment Arrangement, Tranche Two [Member] | Cliff Vesting Schedule [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years    
Performance Stock Units PSU [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Granted in period 1,079,621    
Performance Stock Units PSU [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of tranches | Item 2    
Performance Stock Units PSU [Member] | Omnibus Incentive Plan [Member] | Share-based Payment Arrangement, Tranche One [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of tranches based on Joint Venture compound annual revenue growth rate | Item 1    
Period of calculation for compound annual revenue growth rate 3 years    
Performance Stock Units PSU [Member] | Omnibus Incentive Plan [Member] | Share-based Payment Arrangement, Tranche Two [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of tranches based on Joint Venture compound annual adjusted EBITDA growth rate | Item 1    
Period of calculation for compound annual adjusted EBITDA growth rate 3 years    
Cash Settled Restricted Stock Units CSRSU [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Granted in period 597,006    
Deferred Stock Units DSU [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Granted in period 45,704    
Vesting percentage 100.00%    
Minimum [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Maximum [Member] | Omnibus Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 4 years