Stockholders' equity (deficit) Dividends (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 30, 2017	Dec. 31, 2016	Dec. 26, 2015
Equity [Abstract]
Dividend per share of common stock paid (in dollars per share)	$ 0.32	$ 0.32	$ 0.32	$ 0.32	$ 0.30	$ 0.30	$ 0.30	$ 0.30
Dividends paid on common stock	$ 29,092	$ 29,064	$ 29,226	$ 29,621	$ 27,377	$ 27,475	$ 27,456	$ 27,395	$ 117,003	$ 109,703	$ 100,516
Dividend declared, payment date	Dec. 06, 2017	Sep. 06, 2017	Jun. 14, 2017	Mar. 22, 2017	Nov. 30, 2016	Aug. 31, 2016	Jun. 08, 2016	Mar. 16, 2016