{n. phr.} In a job or position for so long that one is taken entirely for granted, like a part of the physical surroundings. * /He has been working in the same office for so many years now that people consider him to be a part of the furniture./
PART OF THE FURNITURE
Meaning of PART OF THE FURNITURE in English
Dictionary of English idioms . Словарь английских идиом. 2012