Condensed Consolidating Guarantor Financial Statements - Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 65,856	$ 74,216	$ 72,489	$ 58,096
Accounts receivable, net	477,046	418,339
Receivable from affiliates	12,926	25,455
Inventories	102,405	99,234
Other current assets	14,537	18,630
Total current assets	672,770	635,874
Property, plant and equipment, net	1,834,400	1,762,072
Equity method investments	432,389	434,289
Goodwill	34,644	34,230
Other intangible assets, net	148,350	150,978
Other noncurrent assets	54,173	57,529
Total assets	3,176,726	3,074,972
Current liabilities:
Accounts Payable	417,586	367,307
Due to Related Parties	17,086	26,508
Accrued Liabilities	87,368	81,104
Total current liabilities	535,822	488,355
Long-term debt, net	1,140,637	1,050,918
Deferred income taxes	59,921	64,501
Other noncurrent liabilities	26,001	25,233
Commitments and contingencies
Total owners’ equity	1,414,345	1,445,965
Total liabilities and owners’ equity	3,176,726	3,074,972
Other current liabilities including deferred revenue and current portion of long-term debt	13,782	13,436
Parent Company [Member]
Current assets:
Cash and cash equivalents	8,214	19,002	2,608	4,559
Accounts receivable, net	48	0
Receivable from affiliates	28	27
Inventories	0	0
Other current assets	5,299	8,986
Total current assets	13,589	28,015
Property, plant and equipment, net	7,012	5,621
Equity method investments	2,518,858	2,454,118
Goodwill	0	0
Other intangible assets, net	14	15
Other noncurrent assets	49,810	54,155
Total assets	2,589,283	2,541,924
Current liabilities:
Accounts Payable	855	674
Due to Related Parties	0	0
Accrued Liabilities	20,174	25,078
Total current liabilities	22,194	26,641
Long-term debt, net	1,140,619	1,050,893
Deferred income taxes	9,752	16,119
Other noncurrent liabilities	2,373	2,306
Commitments and contingencies
Total owners’ equity	1,414,345	1,445,965
Total liabilities and owners’ equity	2,589,283	2,541,924
Other current liabilities including deferred revenue and current portion of long-term debt	1,165	889
Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	0	0	10,671	9,058
Accounts receivable, net	415,704	361,160
Receivable from affiliates	12,148	25,244
Inventories	90,564	89,638
Other current assets	5,452	5,760
Total current assets	523,868	481,802
Property, plant and equipment, net	951,187	970,079
Equity method investments	1,005,151	940,696
Goodwill	26,628	26,628
Other intangible assets, net	147,086	149,669
Other noncurrent assets	1,882	2,080
Total assets	2,655,802	2,570,954
Current liabilities:
Accounts Payable	399,406	348,297
Due to Related Parties	17,086	26,508
Accrued Liabilities	24,364	23,423
Total current liabilities	447,068	403,336
Long-term debt, net	6,210	6,142
Deferred income taxes	0	0
Other noncurrent liabilities	0	0
Commitments and contingencies
Total owners’ equity	2,202,524	2,161,476
Total liabilities and owners’ equity	2,655,802	2,570,954
Other current liabilities including deferred revenue and current portion of long-term debt	6,212	5,108
Non-Guarantor Subsidiaries [Member]
Current assets:
Cash and cash equivalents	62,087	59,796	61,298	46,043
Accounts receivable, net	61,294	57,179
Receivable from affiliates	750	184
Inventories	11,841	9,596
Other current assets	3,786	3,887
Total current assets	139,758	130,642
Property, plant and equipment, net	876,201	786,372
Equity method investments	0	0
Goodwill	8,016	7,602
Other intangible assets, net	1,250	1,294
Other noncurrent assets	2,481	1,294
Total assets	1,027,706	927,204
Current liabilities:
Accounts Payable	17,325	18,336
Due to Related Parties	0	0
Accrued Liabilities	42,829	32,603
Total current liabilities	66,559	58,378
Long-term debt, net	16,500	16,500
Deferred income taxes	50,169	48,382
Other noncurrent liabilities	23,628	22,927
Commitments and contingencies
Total owners’ equity	870,850	781,017
Total liabilities and owners’ equity	1,027,706	927,204
Other current liabilities including deferred revenue and current portion of long-term debt	6,405	7,439
Consolidating Adjustments [Member]
Current assets:
Cash and cash equivalents	(4,445)	(4,582)	$ (2,088)	$ (1,564)
Accounts receivable, net	0	0
Receivable from affiliates	0	0
Inventories	0	0
Other current assets	0	(3)
Total current assets	(4,445)	(4,585)
Property, plant and equipment, net	0	0
Equity method investments	(3,091,620)	(2,960,525)
Goodwill	0	0
Other intangible assets, net	0	0
Other noncurrent assets	0	0
Total assets	(3,096,065)	(2,965,110)
Current liabilities:
Accounts Payable	0	0
Due to Related Parties	0	0
Accrued Liabilities	1	0
Total current liabilities	1	0
Long-term debt, net	(22,692)	(22,617)
Deferred income taxes	0	0
Other noncurrent liabilities	0	0
Commitments and contingencies
Total owners’ equity	(3,073,374)	(2,942,493)
Total liabilities and owners’ equity	(3,096,065)	(2,965,110)
Other current liabilities including deferred revenue and current portion of long-term debt	$ 0	$ 0