Share-Based Compensation - RSU and RSA activity (Details) - USD ($) $ in Millions		12 Months Ended
	Sep. 25, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
RSUs
RSU and RSA activity ( including Performance RSUs and RSAs)
Outstanding at beginning of year		2,897,758	3,609,118	2,988,041
Granted (in shares)	987,496	1,772,263	1,165,578	2,344,034
Released (in shares)		(1,405,294)	(1,420,485)	(1,185,905)
Forfeited (in shares)		(195,324)	(456,453)	(537,052)
Outstanding at end of year		3,069,403	2,897,758	3,609,118
Additional disclosures
Aggregate intrinsic value outstanding		$ 78.5
Total estimated fair value of RSUs vested		31.6	$ 25.1	$ 21.4
RSAs
Additional disclosures
Aggregate intrinsic value outstanding		$ 25.0
Performance-Contingent Awards - RSAs
RSU and RSA activity ( including Performance RSUs and RSAs)
Outstanding at beginning of year		1,305,000	1,440,000	0
Granted (in shares)		0	0	1,575,000
Released (in shares)		(326,250)	0	0
Forfeited (in shares)		0	(135,000)	(135,000)
Outstanding at end of year		978,750	1,305,000	1,440,000