Summary of significant accounting policies - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Accounting Policies [Abstract]
Cash and cash equivalents	$ 1,018,317	$ 361,425
Restricted cash	94,047	69,746
Restricted cash, included in Other assets	1,735	661
Total cash, cash equivalents, and restricted cash	$ 1,114,099	$ 431,832	$ 333,115	$ 208,358