Leases Assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 31, 2018
Assets and Liabilities, Lessee [Abstract]
Operating lease assets	$ 36,307	$ 0
Finance lease assets	3,939
Total leased assets	40,246
Current operating leases liabilities	12,325	0
Non-current operating leases liabilities	24,034	0
Total operating lease liabilities	36,359
Current portion of finance leases liabilities	(1,409)
Non-current finance leases liabilities	2,079	$ 2,862
Total finance lease liabilities	3,488
Total lease liabilities	$ 39,847