Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 30, 2019	Dec. 29, 2018	Dec. 30, 2017	Dec. 30, 2018
Lessee, Lease, Description [Line Items]
Leases renewal term (up to)	5 years
Leases termination period (within)	1 year
Operating lease right-of-use assets	$ 27,868	$ 0
Total lease liabilities	$ 30,403	0
Operating leases, the weighted-average remaining lease term	6 years 6 months
Operating leases, weighted-average discount rate	7.00%
Operating leases obligation for previously restructured facilities	$ 8,100
Operating leases, rental expense		$ 8,300	$ 8,900
Minimum
Lessee, Lease, Description [Line Items]
Leases remaining term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Leases remaining term	8 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets				$ 29,900
Total lease liabilities				$ 32,300