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Acquisitions Acquisitions (Details) - USD ($) $ in Thousands	Jul. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill		$ 257,302	$ 34,230	$ 48,032	$ 58,326
HFOTCO LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 3,583
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	11,101
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	5,277
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	1,327,168
Goodwill	257,302
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	72,392
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	1,967,823
Payments to Acquire Businesses, Gross	297,822
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	330,341
Interest rate swaps acquired through acquisition (Note 5)	549,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	9,876
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt	5,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	760,500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	13,884
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	789,760
Business Combination, Consideration Transferred	1,967,823
Customer Contracts [Member] \| HFOTCO LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	1,000
Customer Relationships [Member] \| HFOTCO LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	260,000
Noncompete Agreements [Member] \| HFOTCO LLC [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	$ 30,000