Lease Commitments - Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 28, 2019	Sep. 28, 2019
Leases [Abstract]
Short-term lease expenses	$ 86	$ 387
Variable lease expenses	239	621
Operating lease rent expenses	2,131	6,539
Total operating lease costs	$ 2,456	$ 7,547