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Interest Expense (Details) - USD ($) $ in Thousands	1 Months Ended	5 Months Ended	6 Months Ended		12 Months Ended
	Aug. 14, 2015	Dec. 31, 2015	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Interest and Debt Expense [Abstract]
Interest incurred on debt		$ 7,694	$ 35,473	$ 12,086	$ 24,060	$ 20,408
Interest Expense, Related Party			5,090	0
Senior Note redemption premium			4,782	0
Accretion of fair value adjustment on Senior Notes			19,414	3,208
Accretion of original issue discount on 2018 Term Loans	$ 268	2,305	357	0	6,454	6,305
Amortization of debt issuance costs			1,416	154	309	201
Total interest expense		$ 9,999	$ 66,532	$ 15,448	$ 30,823	$ 26,914
Effective interest rate, revolving credit facility			5.59%		4.57%	5.52%
Stated interest rate					6.375%
Accelerated Accretion			$ 18,700

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Accelerated Accretion on Extinguished Debt

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Accretion Expense on Extinguished Debt

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Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

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Amount of amortization expense attributable to debt issuance costs.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Amount of interest expense incurred on a debt or other obligation to related party.

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The effective interest rate during the reporting period.

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The excess of the (1) fair value of consideration transferred to the holders of a security in excess of (2) the carrying amount of the security reported on the registrant's balance sheet, which will be deducted from net earnings to derive net earnings available to common shareholders. This amount is generally an adjustment considered in the computation of earnings per share.

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