Debt and Credit Facility Debt Obligations (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Feb. 28, 2017	Feb. 28, 2015
Debt Instrument [Line Items]
Long-term debt, gross	$ 4,513,800	$ 4,513,800
Total Convertible Debt	4,513,800	4,513,800
Less: Debt discount	(1,473,900)	(1,516,500)
Less: Debt issuance costs	(44,700)	(46,800)	$ (33,700)
Net long-term debt including current maturities	2,995,200	2,950,500
Current portion of long-term debt	(11,256)	(49,952)
Net long-term debt	2,983,908	2,900,524
December 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020
Debt Instrument [Line Items]
Credit Facility	0	0
Less: Debt issuance costs	$ (7,700)	(8,500)
2017 Senior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	1.625%
Effective Interest Rate	6.00%
Fair Value of Liability Component at Issuance (1)	$ 1,396,300
Long-term debt, gross	2,070,000	2,070,000
Less: Debt discount	(654,900)	(667,500)
Less: Debt issuance costs	$ (17,300)	(17,600)
2015 Senior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	1.625%
Effective Interest Rate	5.90%
Fair Value of Liability Component at Issuance (1)	$ 1,160,100
Long-term debt, gross	1,725,000	1,725,000
Less: Debt discount	(435,300)	(446,600)
Less: Debt issuance costs	$ (16,200)	(16,600)
2017 Junior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	2.25%
Effective Interest Rate	7.40%
Fair Value of Liability Component at Issuance (1)	$ 321,100
Long-term debt, gross	686,300	575,000
Less: Debt discount	(362,600)	(309,300)
Less: Debt issuance costs	$ (3,400)	(3,400)		$ (30,300)
2007 Junior Subordinated Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	2.125%
Effective Interest Rate	9.10%
Fair Value of Liability Component at Issuance (1)	$ 11,500
Long-term debt, gross	32,500	143,800
Less: Debt discount	(21,100)	(93,100)
Less: Debt issuance costs	$ (100)	$ (700)