Summary of Significant Accounting Policies - Reconciliation of Liabilities (Details) - Fair value, inputs, level 3 - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 3,300	$ 3,200
Settlement of milestone #1	(1,446)
Change in fair value measurement	546	100
Ending balance	$ 2,400	$ 3,300	$ 3,200
SafeOp Surgical, Inc.
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Contingent consideration liability recorded upon acquisition of SafeOp			$ 3,200