Fair Value Measurements (Carrying Amount and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021
Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 80,414	$ 113,101
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	80,414	113,101
Senior Notes due March 1, 2025 [Member] | Significant Other Observable Inputs (Level 2) | Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	1,318,876	1,318,079
Senior Notes due March 1, 2025 [Member] | Significant Other Observable Inputs (Level 2) | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	1,338,250	1,351,500
Senior Amortizing Notes due June 30, 2022 [Member] | Significant Other Observable Inputs (Level 2) | Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt component of tangible equity units	12,470	20,345
Senior Amortizing Notes due June 30, 2022 [Member] | Significant Other Observable Inputs (Level 2) | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt component of tangible equity units	12,896	21,435
Senior Credit Facilities [Member] | Significant Other Observable Inputs (Level 2) | Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	3,321,963	3,405,552
Senior Credit Facilities [Member] | Significant Other Observable Inputs (Level 2) | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 3,389,178	$ 3,488,883