Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Mar. 31, 2015
Senior Subordinated Convertible Debenture Due 2025 [Member] | Estimate of Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Disclosure for Subordinated Convertible Debentures	$ 1,637,767	$ 1,787,531
Senior Subordinated Convertible Debenture Due 2025 [Member] | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Disclosure for Subordinated Convertible Debentures	1,197,792	1,174,036
Junior Subordinated Convertible Debentures Due 2037 Member | Estimate of Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Disclosure for Subordinated Convertible Debentures	1,000,673	1,124,125
Junior Subordinated Convertible Debentures Due 2037 Member | Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Disclosure for Subordinated Convertible Debentures	$ 193,630	$ 190,870