Fair Value Measurements (Carrying Amount and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020
Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 137,357	$ 410,405
Accounts receivable	697,948	740,105
Investment in business purchase option		146,500
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	137,357	410,405
Accounts receivable	697,948	740,105
Investment in business purchase option		146,500
Significant Other Observable Inputs (Level 2) | Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt component of tangible equity units	24,268	35,431
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	24,801	34,806
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	1,317,689	997,772
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	1,348,188	950,000
Senior Credit Facilities [Member] | Significant Other Observable Inputs (Level 2) | Carrying [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	3,447,156	3,682,457
Senior Credit Facilities [Member] | Significant Other Observable Inputs (Level 2) | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 3,529,963	$ 3,452,687