Income taxes - Components of Provision (Benefit) For Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Current:
Federal	$ 102,349	$ 97,972	$ 90,586
State	27,922	28,430	23,694
Foreign	3,094	3,808	3,186
Current tax provision	133,365	130,210	117,466
Deferred:
Federal	(145,903)	(9,983)	(19,034)
State	(791)	(3,152)	(3,060)
Foreign	1,707	598	987
Deferred tax benefit	(144,987)	(12,537)	(21,107)
Provision for income taxes	$ (11,622)	$ 117,673	$ 96,359