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Summary of Cash-Based Performance Plan Unit Activity (Detail) - $ / shares
12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Weighted-average Grant-Date Fair Value, Beginning Balance Outstanding $ 23.58 $ 39.53 $ 48.68
Weighted-average Grant-Date Fair Value, Granted   6.83 19.14
Weighted-average Grant-Date Fair Value, Ending Balance Outstanding $ 24.19 $ 23.58 $ 39.53
Number of Shares Beginning Balance Outstanding 363,630 185,060 146,388
Number of Shares, Granted   168,380 56,370
Number of Shares Ending Balance Outstanding 350,838 363,630 185,060
Cash-based Performance Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Weighted-average Grant-Date Fair Value, Beginning Balance Outstanding $ 1.16 $ 1.10  
Weighted-average Grant-Date Fair Value, Granted   1.22 $ 1.10
Weighted-average Grant-Date Fair Value, Cancelled/forfeited 1.15 1.10  
Weighted-average Grant-Date Fair Value, Ending Balance Outstanding $ 1.16 $ 1.16 $ 1.10
Number of Shares Beginning Balance Outstanding 7,913,716 4,519,703  
Number of Shares, Granted   3,527,333 4,519,703
Number of Shares, Cancelled/forfeited (179,991) (133,320)  
Number of Shares Ending Balance Outstanding 7,733,725 7,913,716 4,519,703