Condensed Consolidating Financial Information - Balance Sheet (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents		$ 347,525	$ 336,997	$ 190,556	$ 264,093
Short-term investments		41,033	28,369
Accounts receivable, net		775,137	698,477
Inventory, net		166,827	166,307
Assets held for sale		20,289	37,052
Other current assets		188,229	180,134
Total current assets		1,539,040	1,447,336
Property, plant and equipment, net		5,608,948	6,109,565
Goodwill		172,976	173,226
Deferred income taxes		407,851	419,003
Other long-term assets		231,732	252,854
Total assets (1)	[1]	7,960,547	8,401,984
Current liabilities:
Less: current portion		433	181
Trade accounts payable		331,713	363,416
Accrued liabilities		392,476	533,044
Income taxes payable		27,770	22,835
Total current liabilities		752,392	919,476
Long-term debt		3,737,273	4,027,766
Other long-term liabilities		272,607	301,633
Deferred income taxes		23,782	10,338
Total liabilities (1)	[1]	4,786,054	5,259,213
Redeemable noncontrolling interest in subsidiary (Note 3)		210,665	203,998
Shareholders' equity		2,931,222	2,911,816
Noncontrolling interest		32,606	26,957
Total equity		2,963,828	2,938,773	$ 2,927,221	$ 3,254,795
Total liabilities and equity		7,960,547	8,401,984
Consolidating Adjustments
Current assets:
Intercompany receivables		(475,124)	(614,694)
Investment in consolidated affiliates		(12,335,978)	(12,131,052)
Deferred income taxes		(376,767)	(333,349)
Other long-term assets		(19,325)	(72,143)
Total assets (1)		(13,207,194)	(13,151,238)
Current liabilities:
Long-term debt		(19,325)	(72,143)
Deferred income taxes		(376,767)	(333,349)
Intercompany payable		(475,124)	(614,694)
Total liabilities (1)		(871,216)	(1,020,186)
Shareholders' equity		(12,335,978)	(12,131,052)
Total equity		(12,335,978)	(12,131,052)
Total liabilities and equity		(13,207,194)	(13,151,238)
Parent Company | Reportable Legal Entities
Current assets:
Cash and cash equivalents		769	1,091
Other current assets		50	50
Total current assets		819	1,141
Intercompany receivables		92,611	133,602
Investment in consolidated affiliates		2,867,184	2,799,320
Total assets (1)		2,960,614	2,934,063
Current liabilities:
Trade accounts payable		173	147
Accrued liabilities		29,219	21,100
Total current liabilities		29,392	21,247
Intercompany payable			1,000
Total liabilities (1)		29,392	22,247
Shareholders' equity		2,931,222	2,911,816
Total equity		2,931,222	2,911,816
Total liabilities and equity		$ 2,960,614	2,934,063
Guarantor Subsidiaries
Condensed Consolidating Financial Information
Ownership percentage		100.00%
Guarantor Subsidiaries | Reportable Legal Entities
Current assets:
Cash and cash equivalents		$ 42	44
Other current assets			56
Total current assets		42	100
Intercompany receivables		382,513	481,092
Investment in consolidated affiliates		5,416,336	5,531,799
Deferred income taxes		376,767	333,349
Other long-term assets		173	78
Total assets (1)		6,175,831	6,346,418
Current liabilities:
Trade accounts payable		152	124
Accrued liabilities		20,248	67,760
Total current liabilities		20,400	67,884
Long-term debt		3,756,598	4,099,909
Other long-term liabilities		16,306	16,284
Total liabilities (1)		3,793,304	4,184,077
Shareholders' equity		2,382,527	2,162,341
Total equity		2,382,527	2,162,341
Total liabilities and equity		6,175,831	6,346,418
Other Subsidiaries (Non-Guarantors) | Reportable Legal Entities
Current assets:
Cash and cash equivalents		346,714	335,862
Short-term investments		41,033	28,369
Accounts receivable, net		775,137	698,477
Inventory, net		166,827	166,307
Assets held for sale		20,289	37,052
Other current assets		188,179	180,028
Total current assets		1,538,179	1,446,095
Property, plant and equipment, net		5,608,948	6,109,565
Goodwill		172,976	173,226
Investment in consolidated affiliates		4,052,458	3,799,933
Deferred income taxes		407,851	419,003
Other long-term assets		250,884	324,919
Total assets (1)		12,031,296	12,272,741
Current liabilities:
Less: current portion		433	181
Trade accounts payable		331,388	363,145
Accrued liabilities		343,009	444,184
Income taxes payable		27,770	22,835
Total current liabilities		702,600	830,345
Other long-term liabilities		256,301	285,349
Deferred income taxes		400,549	343,687
Intercompany payable		475,124	613,694
Total liabilities (1)		1,834,574	2,073,075
Redeemable noncontrolling interest in subsidiary (Note 3)		210,665	203,998
Shareholders' equity		9,953,451	9,968,711
Noncontrolling interest		32,606	26,957
Total equity		9,986,057	9,995,668
Total liabilities and equity		$ 12,031,296	$ 12,272,741

[1] The condensed consolidated balance sheet as of September 30, 2018 and December 31, 2017 include assets and liabilities of variable interest entities. See Note 3—Joint Ventures for additional information.