Quarterly financial data (unaudited) (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
Income Statement [Abstract]
Total revenues	$ 227,139	$ 224,168	$ 218,522	$ 190,672	$ 215,705	$ 207,099	$ 216,309	$ 189,776	$ 860,501	$ 828,889	$ 810,933
Operating income	120,126	122,033	113,550	91,293	113,880	109,360	106,141	85,333	447,002	414,714	319,567
Net income (loss)	$ 195,492	$ 52,246	$ 55,704	$ 47,467	$ 56,120	$ 52,712	$ 49,590	$ 37,154	$ 350,909	$ 195,576	$ 105,227
Common-basic (in dollars per share)	$ 2.17	$ 0.58	$ 0.61	$ 0.52	$ 0.61	$ 0.58	$ 0.54	$ 0.41	$ 3.86	$ 2.14	$ 1.10
Common-diluted (in dollars per share)	$ 2.13	$ 0.57	$ 0.60	$ 0.51	$ 0.61	$ 0.57	$ 0.54	$ 0.40	$ 3.80	$ 2.11	$ 1.08