Debt and Credit Facilities (Borrowing Obligations) (Detail) - USD ($) $ in Thousands		1 Months Ended
	Mar. 01, 2017	Mar. 31, 2020	Nov. 30, 2017	Jun. 30, 2020	Sep. 30, 2019	Dec. 22, 2016	Jun. 21, 2016
Debt Instrument [Line Items]
Long-Term Debt, Maturity, Year One				$ 0
Long-Term Debt, Maturity, Year Two				0
Long-Term Debt, Maturity, Year Three				227,395
Long-Term Debt, Maturity, Year Four				676,488
Long-Term Debt, Maturity, Year Five				0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five				762,656
Total debt				1,524,825	$ 1,936,406
Less: current portion (a)				0	(1,142,870)
Total long-term debt				1,524,825	793,536
Debt Issuance Costs, Noncurrent, Net				(262)	(511)
Long-term Debt, Gross				1,666,539
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net				(141,714)
5.625% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Senior Notes, net of unamortized premium				495,994	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				601,593	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	$ 17,800	$ 46,600	$ 331,200
1.25% Convertible Debentures due 2025 [Member]
Debt Instrument [Line Items]
Convertible Debentures, net of unamortized discount				213,283	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				214,217	$ 240,406
Senior Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt, Maturity, Year One				0
Long-Term Debt, Maturity, Year Two				0
Long-Term Debt, Maturity, Year Three				0
Long-Term Debt, Maturity, Year Four				0
Long-Term Debt, Maturity, Year Five				0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five				500,000
Total debt				495,732
Long-term Debt, Gross				500,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net				(4,268)
Convertible Debt [Member]
Debt Instrument [Line Items]
Long-Term Debt, Maturity, Year One				0
Long-Term Debt, Maturity, Year Two				0
Long-Term Debt, Maturity, Year Three				227,395
Long-Term Debt, Maturity, Year Four				676,488
Long-Term Debt, Maturity, Year Five				0
Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five				262,656
Total debt				1,029,093
Long-term Debt, Gross				1,166,539
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net				$ (137,446)