Equity method investments Summarized Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Equity Method Investments and Joint Ventures [Abstract]
Current assets	$ 363,277	$ 300,999
Current liabilities	140,113	120,611
Working capital	223,164	180,388
Property, plant, and equipment, net	165,442	153,038
Other assets	139,958	124,676
Long-term liabilities	48,429	48,460
Equity of equity method investments	480,135	409,642
Equity method, revenues	646,269	629,717	$ 622,982
Equity method, gross profit	345,302	329,206	327,684
Equity method, net income	$ 33,791	$ 32,529	$ 33,650