Revenue Recognition (Tables)  | 
3 Months Ended | ||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2019  | |||||||||||||||||||||||||||||
| Revenue from Contract with Customer [Abstract] | |||||||||||||||||||||||||||||
| Contract with Customer, Asset and Liability | 
 
The following table presents changes in these contract liability balances for the three-month period ended March 31, 2019 (U.S. dollars in thousands):
 
 The table above excludes liability for sales returns, as they are insignificant.  
 | 
||||||||||||||||||||||||||||
| X | ||||||||||
- Definition Tabular disclosure of contract balances and changes in contract balances. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- References No definition available. 
  |