New accounting standards (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2017	Jun. 26, 2016	Jul. 02, 2017	Jun. 26, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in net income and cash flows from operating activities due to adoption of new standard			$ 197,690	$ 181,488
Net income	$ 78,003	$ 59,303	$ 118,173	$ 109,992
Net income (in dollars per share)	$ 1.67	$ 1.26	$ 2.53	$ 2.29
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 1,100		$ 4,500
Net income (in dollars per share)	$ 0.02		$ 0.09