Revenues - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenue from External Customer [Line Items]
Fees to GPOs	$ 2,800	$ 2,200	$ 7,600	$ 6,200
Short-term deferred revenues	88,205		88,205		$ 81,835
Deferred revenues recognized	4,800		69,800
Contract with Customer, Liability, Current, Gross					92,900
Long-term deferred revenues	7,979		7,979		10,582
Deferred cost of sale,short-term
Revenue from External Customer [Line Items]
Short-term deferred revenues	$ 14,300		$ 14,300		$ 11,100