Revenues - Revenues by Disaggregated Category (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaborative Arrangement with Ipsen
Disaggregation of Revenue [Line Items]
Total revenues	76,016	57,186	$ 120,133	145,038
GSK \| Collaborative Arrangement with Ipsen
Disaggregation of Revenue [Line Items]
Percent of royalty on net sale			3.00%
Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	191,768	162,946	$ 565,024	443,054
Gross product revenues
Disaggregation of Revenue [Line Items]
Total revenues	239,916	193,356	704,084	525,438
Discounts and allowances
Disaggregation of Revenue [Line Items]
Total revenues	48,148	30,410	139,060	82,384
Total collaboration revenues
Disaggregation of Revenue [Line Items]
Total revenues	79,935	62,451	162,441	182,170
License revenues
Disaggregation of Revenue [Line Items]
Total revenues	68,035	51,323	128,937	152,261
Research and development services revenues
Disaggregation of Revenue [Line Items]
Total revenues	12,988	10,560	35,814	27,464
Other collaboration revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ (1,088)	$ 568	$ (2,310)	$ 2,445