Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	$ (9,530)	$ 336,672
Cash flows from investing activities:
Purchases of investments	(4,489)
Sales and maturities of investments	12,429	367
Capital expenditures	(315,769)	(193,234)
Proceeds from sales of assets and insurance claims	18,796	13,834
Other changes in investing	(384)	38
Net cash (used for) provided by investing activities	(289,417)	(178,995)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts	(42)	294
Proceeds from issuance of long-term debt	411,200
Debt issuance costs	(11,037)
Proceeds from revolving credit facilities	100,000	260,000
Distributions to Non-controlling interest	6,982
Proceeds from (payments for) issuance of common shares	8,300	39
Purchase of capped call hedge transactions	(40,250)
Reduction of long-term debt	(377,983)	(148,045)
Dividends to shareholders	(34,197)	(16,922)
Proceeds from (payments for) commercial paper, net	171,985	(1,500)
Payments on term loan	(162,500)
Proceeds from (payments for) short-term borrowings	(173)	(6,333)
Cash proceeds from equity component of exchangeable debt	159,952
Non-controlling interest contribution	20,000
Other changes	(7,844)	(4,280)
Reduction in revolving credit facilities		(260,000)
Repurchase of common shares		(1,687)
Net cash (used for) provided by financing activities	230,429	(178,434)
Effect of exchange rate changes on cash and cash equivalents	992	(21)
Net increase (decrease) in cash and cash equivalents	(67,526)	(20,778)	$ (67,526)
Cash and cash equivalents, beginning of period	264,093	254,530	254,530
Cash and cash equivalents, end of period	196,567	233,752	264,093
Reportable Legal Entities | Parent Company
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	86,986	4,370
Cash flows from financing activities:
Proceeds from (payments for) issuance of common shares	8,300	39
Dividends to shareholders	(40,155)	(19,903)
Proceeds from issuance of intercompany debt	33,000	24,500
Paydown of intercompany debt	(79,000)
Other changes	(7,844)	(4,281)
Net cash (used for) provided by financing activities	(85,699)	355
Net increase (decrease) in cash and cash equivalents		4,725	1,287
Cash and cash equivalents, beginning of period	1,148	873	873
Cash and cash equivalents, end of period	2,435	5,598	1,148
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	(101,280)	(134,437)
Cash flows from investing activities:
Change in intercompany balances	(290,794)	135,938
Net cash (used for) provided by investing activities	(290,794)	135,938
Cash flows from financing activities:
Proceeds from issuance of long-term debt	411,200
Debt issuance costs	(11,037)
Proceeds from revolving credit facilities	100,000	260,000
Proceeds from parent contributions	18,000
Purchase of capped call hedge transactions	(40,250)
Reduction of long-term debt	(265,437)
Proceeds from (payments for) commercial paper, net	171,985	(1,500)
Payments on term loan	(162,500)
Cash proceeds from equity component of exchangeable debt	159,952
Proceeds from issuance of intercompany debt	20,000
Paydown of intercompany debt	(20,000)
Reduction in revolving credit facilities		(260,000)
Net cash (used for) provided by financing activities	381,913	(1,500)
Net increase (decrease) in cash and cash equivalents		1	(10,161)
Cash and cash equivalents, beginning of period	10,177	10	10
Cash and cash equivalents, end of period	16	11	10,177
Reportable Legal Entities | Other Subsidiaries (Non-Guarantors)
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	90,722	469,720
Cash flows from investing activities:
Purchases of investments	(4,489)
Sales and maturities of investments	12,429	367
Investment in unconsolidated affiliates	(36,000)
Capital expenditures	(315,769)	(193,234)
Proceeds from sales of assets and insurance claims	18,796	13,834
Change in intercompany balances	290,794	(135,938)
Other changes in investing	(384)	38
Net cash (used for) provided by investing activities	(34,623)	(314,933)
Cash flows from financing activities:
Increase (decrease) in cash overdrafts	(42)	294
Distributions to Non-controlling interest	6,982
Proceeds from parent contributions	18,000
Reduction of long-term debt	(112,546)	(148,045)
Proceeds from (payments for) short-term borrowings	(173)	(6,333)
Proceeds from issuance of intercompany debt	(53,000)	(24,500)
Non-controlling interest contribution	20,000
Paydown of intercompany debt	99,000
Payments on parent (Equity or N/P)	(80,000)
Other changes		1
Repurchase of common shares		(1,687)
Net cash (used for) provided by financing activities	(115,743)	(180,270)
Effect of exchange rate changes on cash and cash equivalents	992	(21)
Net increase (decrease) in cash and cash equivalents		(25,504)	(58,652)
Cash and cash equivalents, beginning of period	252,768	253,647	253,647
Cash and cash equivalents, end of period	194,116	228,143	$ 252,768
Consolidating Adjustments
Condensed Consolidating Statements Of Cash Flows
Net cash provided by (used for) operating activities	(85,958)	(2,981)
Cash flows from investing activities:
Investment in unconsolidated affiliates	36,000
Net cash (used for) provided by investing activities	36,000
Cash flows from financing activities:
Proceeds from parent contributions	(36,000)
Dividends to shareholders	5,958	2,981
Payments on parent (Equity or N/P)	80,000
Net cash (used for) provided by financing activities	$ 49,958	$ 2,981