Debt Obligations (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2017	Feb. 28, 2015	Mar. 31, 2017	Mar. 31, 2016
Debt Instrument [Line Items]
Long-term debt, gross			$ 4,513,800	$ 3,352,000
Total Convertible Debt			4,513,800	2,300,000
Amount of unamortized debt discount of debentures			(1,516,500)	(869,000)
Debt issuance amortization	$ (33,700)		(46,800)	(29,600)
Net long-term debt including current maturities			2,950,500	2,453,400
Less: Current maturities			(49,952)	0
Net long-term debt			2,900,524	2,453,405
December 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020
Debt Instrument [Line Items]
Credit Facility			0
Debt issuance amortization			$ (8,500)	(8,800)
2017 Senior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate			1.625%
Effective Interest Rate			6.00%
Estimated fair value of the liability component of the senior subordinated convertible debentures as of the issuance date			$ 1,396,300
Long-term debt, gross			2,070,000	0
Amount of unamortized debt discount of debentures			(667,500)	0
Debt issuance amortization			$ (17,600)	0
2015 Senior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate			1.625%
Effective Interest Rate			5.90%
Estimated fair value of the liability component of the senior subordinated convertible debentures as of the issuance date			$ 1,160,100
Long-term debt, gross			1,725,000	1,725,000
Amount of unamortized debt discount of debentures			(446,600)	(490,300)
Debt issuance amortization			$ (16,600)	(18,400)
2017 Junior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate			2.25%
Effective Interest Rate			7.50%
Estimated fair value of the liability component of the senior subordinated convertible debentures as of the issuance date			$ 264,800
Long-term debt, gross			575,000	0
Amount of unamortized debt discount of debentures			(309,300)	0
Debt issuance amortization		$ (30,300)	$ (3,400)	0
2007 Junior Subordinated Convertible Notes
Debt Instrument [Line Items]
Coupon Interest Rate			2.125%
Effective Interest Rate			9.10%
Estimated fair value of the liability component of the senior subordinated convertible debentures as of the issuance date			$ 41,000
Long-term debt, gross			143,800	575,000
Amount of unamortized debt discount of debentures			(93,100)	(378,700)
Debt issuance amortization			$ (700)	$ (2,400)