Long-Term Debt, Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Jun. 25, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt	$ 995,848		$ 725,986
Unamortized debt issuance costs	(3,442)		(3,184)
Total	992,406		722,802
Bank Notes Payable [Member]
Debt Instrument [Line Items]
Long-term Debt	3		0
Revolving Credit Facility Due June 26, 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 495,845		225,986
Credit facility, expiration date	Jun. 26, 2022
Long term debt, face amount	$ 850,000
Senior Notes Series A Due February 27, 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 150,000		150,000
Credit facility, expiration date	Feb. 27, 2020
Long term debt, face amount	$ 150,000
Senior Notes Series B Due February 27, 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 350,000		350,000
Credit facility, expiration date	Feb. 27, 2023
Long term debt, face amount	$ 350,000
Credit Line Due June 30, 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 0		$ 0
Credit facility, expiration date	Jun. 30, 2019
Long term debt, face amount	$ 10,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long term debt, face amount		$ 550,000