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Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 17, 2017	Mar. 15, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Capital leases	$ 39			$ 51
Long-term Debt and Capital Lease Obligations, Including Current Maturities	1,215,272			1,050,944
less: current portion of long-term debt	28			26
Long-term debt, net	1,215,244			1,050,918
Senior Notes [Member] \| Senior Unsecured Notes due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	0		$ 300,000	300,000
Debt Issuance Costs, Net	0			(3,708)
Long-term Debt	0			296,292
Senior Notes [Member] \| Senior Unsecured Notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	400,000			400,000
Debt Issuance Costs, Net	(5,376)			(5,909)
Long-term Debt	394,624			394,091
Senior Notes [Member] \| Senior unsecured notes due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	350,000			350,000
Debt Instrument, Unamortized Discount	(4,599)			(4,894)
Debt Issuance Costs, Net	(4,262)			(4,596)
Long-term Debt	341,139			340,510
Senior Notes [Member] \| Senior Unsecured Notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	325,000			0
Debt Instrument, Unamortized Discount	(4,843)	$ (5,000)		0
Debt Issuance Costs, Net	(4,687)			0
Long-term Debt	315,470			0
Line of Credit [Member] \| Revolving Credit Facility [Member] \| Corporate Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	164,000			20,000
Line of Credit [Member] \| Revolving Credit Facility [Member] \| SemMexico Credit Facility [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 0			$ 0