Summary of Significant Accounting Policies - Supplemental Cash Flow Items (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Supplemental Disclosures of Cash Flow Information
Interest paid	$ 3,984	$ 2,405
Taxes paid	5	0
Non-cash activities:
Purchases of property and equipment not paid	$ 2,124	$ 3,026