Debt and Credit Facilities (Borrowing Obligations) (Detail) - USD ($) $ in Thousands	1 Months Ended
	Mar. 31, 2020	Nov. 30, 2017	Sep. 30, 2019	Dec. 22, 2016	Jun. 21, 2016
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 230,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	227,395
Long-term Debt, Maturities, Repayments of Principal in Year Four	676,488
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	762,656
Total debt	1,742,859		$ 1,936,406
Less: current portion (a)	(230,000)		(1,142,870)
Total long-term debt	1,512,859		793,536
Debt Issuance Costs, Noncurrent, Net	229,655		511
Long-term Debt, Gross	1,896,539
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	(153,680)
5.625% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Senior Notes, net of unamortized premium	495,839		495,518	$ 500,000
6.0% Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Senior Notes, net of unamortized premium	0		298,529		$ 300,000
Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Senior Notes, net of unamortized premium	594,515		580,639
Convertible Debentures Two Point Seven Five Percent Due November One Twenty Thirty One [Member]
Debt Instrument [Line Items]
Convertible Debentures, net of unamortized discount	0		46,568
Repayments of Debt	46,600	$ 331,200
1.25% Convertible Debentures due 2025 [Member]
Debt Instrument [Line Items]
Convertible Debentures, net of unamortized discount	211,014		275,257
Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Convertible Debentures, net of unamortized discount	211,836		$ 240,406
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	230,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	500,000
Total debt	725,494
Long-term Debt, Gross	730,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	(4,506)
Convertible Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	227,395
Long-term Debt, Maturities, Repayments of Principal in Year Four	676,488
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five	262,656
Total debt	1,017,365
Long-term Debt, Gross	1,166,539
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ (149,174)