Selected Consolidated Financial Statement Information - Accrued Expenses (Details) - USD ($) $ in Thousands			6 Months Ended
	Jul. 01, 2016	Jun. 28, 2016	Dec. 31, 2017	Jun. 30, 2017
Accrued Expenses
Salaries and bonus			$ 6,064	$ 8,247
Commissions			5,600	8,217
Accrued vacation			3,552	3,436
Accrued excise, sales and other taxes			3,407	3,497
Accrued legal				2,600
Legal settlement			1,831	1,814
Clinical studies			456	657
Other accrued expenses			1,770	1,768
Accrued expenses			$ 22,680	$ 30,236
Litigation Settlement, Amount Awarded to Other Party		$ 8,000
Payments for Legal Settlements	$ 3,000
Settlement Payable in Installments	$ 5,000
Litigation Settlement Interest, Percentage			1.80%
Litigation Settlement, Number of Quarterly Installment Payment			11
Department Of Justice Non Insurance Settlement Maximum Payment Amount			$ 2,000