Long-Term Debt (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Aug. 08, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 19, 2016 USD ($)
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 0
Amortization of debt issuance costs	265	$ 259
Unamortized debt issue costs	1,000			$ 1,200
Credit Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity	310,000
Credit agreement available	16,000
Sub-limit which may be used for issuance of letters of credit	$ 15,000
Borrowing base amount					$ 200,000
Commitment fee on unutilized borrowing base	0.50%
Credit agreement, outstanding	$ 184,000
Credit Agreement | Thereafter
Line of Credit Facility [Line Items]
Debt to Adjusted EBITDA ratio	4.5
Credit Facility Maturing March 31, 2020
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 500,000
Lender loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000		$ 200,000
Minimum | Credit Agreement
Line of Credit Facility [Line Items]
Consolidated current asset ratio	1.0
Required interest coverage ratio	2.5
Distribution limitation, credit facility excess over borrowing base (as a percent)	90.00%
Ownership percentage by subsidiary	50
Minimum | Credit Agreement | Scenario One
Line of Credit Facility [Line Items]
Debt to Adjusted EBITDA ratio	4.5
Minimum | Credit Agreement | Scenario Two
Line of Credit Facility [Line Items]
Debt to Adjusted EBITDA ratio	4.0
Minimum | Credit Agreement | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Variable interest rate	2.25%
Minimum | Credit Agreement | ABR
Line of Credit Facility [Line Items]
Variable interest rate	1.25%
Maximum | Credit Agreement | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Variable interest rate	3.25%
Maximum | Credit Agreement | ABR
Line of Credit Facility [Line Items]
Variable interest rate	2.25%