Leases Assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 28, 2019	Dec. 31, 2018
Assets and Liabilities, Lessee [Abstract]
Operating lease assets	$ 40,189	$ 0
Finance lease assets	3,260
Total lease assets	43,449
Current operating lease liabilities	14,159	0
Non-current operating lease liabilities	25,878	0
Total operating lease liabilities	40,037
Current portion of finance lease liabilities	(1,309)
Non-current finance lease liabilities	1,787	$ 2,862
Total finance lease liabilities	3,096
Total lease liabilities	$ 43,133