Enterprise-Wide Disclosures - Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Enterprise-Wide Disclosures
Revenue		$ 93,129	$ 90,260	$ 92,667	$ 82,713	$ 74,644	$ 74,039	$ 75,521	$ 77,006	$ 358,769	$ 301,210	$ 324,893
Long-lived assets		11,592				6,996				11,592	6,996	5,863
Deferred tax assets, net of valuation allowance		767				3,861				767	3,861	6,886
United States [Member]
Enterprise-Wide Disclosures
Revenue										232,178	219,886	253,955
Long-lived assets		3,715				5,206				3,715	5,206	4,280
Deferred tax assets, net of valuation allowance						3,810					3,810	6,886
Belgium [Member]
Enterprise-Wide Disclosures
Revenue	[1]									48,585	$ 39,347	$ 35,995
Threshold for separate geographic disclosure											10.00%	10.00%
Luxembourg [Member]
Enterprise-Wide Disclosures
Revenue	[1]									44,660	$ 36,954	$ 31,441
Threshold for separate geographic disclosure											10.00%	10.00%
Other Countries [Member]
Enterprise-Wide Disclosures
Revenue										33,346	$ 5,023	$ 3,502
Long-lived assets		995				785				995	785	791
Foreign Countries [Member]
Enterprise-Wide Disclosures
Revenue										126,591	$ 81,324	$ 70,938
France [Member]
Enterprise-Wide Disclosures
Long-lived assets	[2]	6,042,000								6,042,000
Threshold for long-lived asset geographic disclosure											10.00%	10.00%
United Kingdom [Member]
Enterprise-Wide Disclosures
Long-lived assets	[3]	840				1,005				840	$ 1,005	$ 792
Threshold for long-lived asset geographic disclosure											10.00%	10.00%
Europe [Member]
Enterprise-Wide Disclosures
Revenue										126,074	$ 81,125	$ 70,629
Deferred tax assets, net of valuation allowance		$ 767				$ 51				$ 767	$ 51

[1] Revenue for our Belgium and Luxembourg operations has been disclosed separately as it exceeds 10% of consolidated revenue in at least one of the years presented.

[2] Long-lived assets for our France operations has been disclosed separately as it exceeds 10% of consolidated long-lived assets in at least one of the years presented.

[3] Long-lived assets for our United Kingdom operations has been disclosed separately as it exceeds 10% of consolidated long-lived assets in at least one of the years presented.