Deferred revenue (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Revenue Recognition [Abstract]
Short-term deferred revenue	$ 95,709	$ 78,774
Deferred service revenue, cost of sales, current		16,900	$ 15,700
Long-term deferred revenue	$ 8,806	$ 10,623

Contract with Customer, Liability, Deferred Revenue, Noncurrent

No definition available.

Name:	omcl_ContractwithCustomerLiabilityDeferredRevenueNoncurrent
Namespace Prefix:	omcl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant