Fair value measurement - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
NeoTract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Milestone payment	$ 106.8
Essential Medical, Inc.
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Milestone payment	$ 30.0

Amount of cash outflow, made soon after acquisition date of business combination, to settle contingent consideration liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

Name:	us-gaap_PaymentForContingentConsiderationLiabilityInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration