Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended
	Jul. 03, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities			$ 77,357	$ (9,530)
Cash flows from investing activities:
Purchases of investments			(676)	(4,489)
Sales and maturities of investments			2,602	12,429
Capital expenditures			(209,471)	(315,769)
Proceeds from sales of assets and insurance claims			77,272	18,796
Net cash (used for) provided by investing activities			(130,273)	(289,033)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts			(344)	(42)
Debt issuance costs			(12,990)	(11,037)
Proceeds from (payments for) issuance of common shares		$ 21,800	302,014	8,300
Reduction of long-term debt			(460,837)	(377,983)
Dividends to shareholders	$ (21,500)		(36,200)	(34,197)
Proceeds from (payments for) commercial paper, net			(40,000)	171,985
Purchase of capped call hedge transactions				(40,250)
Proceeds from revolving credit facilities			625,000	100,000
Reduction in revolving credit facilities			(1,135,000)
Proceeds from (payments for) short-term borrowings			62	(173)
Proceeds from issuance of preferred stock, net of issuance costs			278,573
Proceeds from issuance of long-term debt			800,000	411,200
Payments on term loan				(162,500)
Cash proceeds from equity component of exchangeable debt				159,952
Noncontrolling interest contribution				20,000
Distributions to noncontrolling interest			(4,676)	(6,982)
Other changes			(3,688)	(7,844)
Net cash (used for) provided by financing activities			311,914	230,429
Effect of exchange rate changes on cash and cash equivalents			(3,637)	992
Net increase (decrease) in cash and cash equivalents			255,361	(67,142)
Cash, cash equivalents and restricted cash, beginning of period			342,029	264,990
Cash, cash equivalents and restricted cash, end of period		597,390	597,390	197,848
Consolidating Adjustments
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities			(28,149)	(85,958)
Cash flows from investing activities:
Cash paid for investments in consolidated affiliates			786,500	36,000
Net cash (used for) provided by investing activities			786,500	36,000
Cash flows from financing activities:
Dividends to shareholders			6,149	5,958
Proceeds from parent contributions			(786,500)	(36,000)
Distribution from subsidiary to parent			22,000	80,000
Net cash (used for) provided by financing activities			(758,351)	49,958
Parent Company | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities			56,041	86,986
Cash flows from investing activities:
Cash paid for investments in consolidated affiliates			(587,500)
Net cash (used for) provided by investing activities			(587,500)
Cash flows from financing activities:
Proceeds from (payments for) issuance of common shares			302,014	8,300
Dividends to shareholders			(42,349)	(40,155)
Proceeds from issuance of intercompany debt			20,000	33,000
Proceeds from issuance of preferred stock, net of issuance costs			278,573
Paydown of intercompany debt			(21,000)	(79,000)
Other changes			(3,688)	(7,844)
Net cash (used for) provided by financing activities			533,550	(85,699)
Net increase (decrease) in cash and cash equivalents			2,091	1,287
Cash, cash equivalents and restricted cash, beginning of period			1,091	1,148
Cash, cash equivalents and restricted cash, end of period		3,182	3,182	2,435
Guarantor Subsidiaries | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities			(102,233)	(101,280)
Cash flows from investing activities:
Change in intercompany balances			127,059	(290,794)
Net cash (used for) provided by investing activities			127,059	(290,794)
Cash flows from financing activities:
Debt issuance costs			(12,990)	(11,037)
Reduction of long-term debt			(460,837)	(265,437)
Proceeds from (payments for) commercial paper, net			(40,000)	171,985
Proceeds from issuance of intercompany debt				20,000
Purchase of capped call hedge transactions				(40,250)
Proceeds from revolving credit facilities			625,000	100,000
Reduction in revolving credit facilities			(1,135,000)
Proceeds from issuance of long-term debt			800,000	411,200
Payments on term loan				(162,500)
Paydown of intercompany debt				(20,000)
Cash proceeds from equity component of exchangeable debt				159,952
Proceeds from parent contributions			199,000	18,000
Net cash (used for) provided by financing activities			(24,827)	381,913
Net increase (decrease) in cash and cash equivalents			(1)	(10,161)
Cash, cash equivalents and restricted cash, beginning of period			44	10,177
Cash, cash equivalents and restricted cash, end of period		43	43	16
Other Subsidiaries (Non-Guarantors) | Reportable Legal Entities
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities			151,698	90,722
Cash flows from investing activities:
Purchases of investments			(676)	(4,489)
Sales and maturities of investments			2,602	12,429
Cash paid for investments in consolidated affiliates			(199,000)	(36,000)
Capital expenditures			(209,471)	(315,769)
Proceeds from sales of assets and insurance claims			77,272	18,796
Change in intercompany balances			(127,059)	290,794
Net cash (used for) provided by investing activities			(456,332)	(34,239)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts			(344)	(42)
Reduction of long-term debt				(112,546)
Proceeds from issuance of intercompany debt			(20,000)	(53,000)
Proceeds from (payments for) short-term borrowings			62	(173)
Paydown of intercompany debt			21,000	99,000
Noncontrolling interest contribution				20,000
Distributions to noncontrolling interest			(4,676)	(6,982)
Proceeds from parent contributions			587,500	18,000
Distribution from subsidiary to parent			(22,000)	(80,000)
Net cash (used for) provided by financing activities			561,542	(115,743)
Effect of exchange rate changes on cash and cash equivalents			(3,637)	992
Net increase (decrease) in cash and cash equivalents			253,271	(58,268)
Cash, cash equivalents and restricted cash, beginning of period			340,894	253,665
Cash, cash equivalents and restricted cash, end of period		$ 594,165	$ 594,165	$ 195,397