Leases Assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 28, 2020	Dec. 31, 2019
Assets and Liabilities, Lessee [Abstract]
Operating lease assets	$ 49,787	$ 40,033
Finance lease assets	2,832	3,183
Total lease assets	52,619	43,216
Current operating lease liabilities	16,920	14,665
Non-current operating lease liabilities	32,712	25,200
Total operating lease liabilities	49,632	39,865
Current portion of finance lease liabilities	(1,332)	(1,348)
Non-current finance lease liabilities	1,104	1,795
Total finance lease liabilities	2,436	3,143
Total lease liabilities	$ 52,068	$ 43,008