Credit Agreement (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 30, 2017
Line of Credit Facility [Line Items]
Borrowings under revolving credit facility	$ 182,500	$ 24,500
February 2018 Amendment [Member]
Line of Credit Facility [Line Items]
Current borrowing capacity	300,000
Maximum Borrowing Capacity	$ 450,000
Expiration Date	Feb. 14, 2023
Borrowings under revolving credit facility	$ 182,500
Letters of Credit Outstanding	3,450
Remaining Borrowing Capacity	$ 114,050
Weighted-Average Interest Rate at Period End	3.60%
March 2017 Amendment [Member]
Line of Credit Facility [Line Items]
Borrowings under revolving credit facility		24,500
Letters of Credit Outstanding		3,150
Remaining Borrowing Capacity		$ 125,500
Weighted-Average Interest Rate at Period End		3.10%