Fair Value Measurements - Derivatives (Details)
9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Put Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Term (in years) 4 years 9 months 5 years 6 months
Call Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Term (in years) 4 years 9 months 5 years 6 months
Interest rate volatility | Put Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.176 0.210
Interest rate volatility | Call Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.176 0.210
Market yield rate | Put Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.130 0.125
Market yield rate | Call Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.130 0.125
Dividend yield | Put Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.000 0.000
Dividend yield | Call Option Liability (Madryn)    
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative liability 0.000 0.000