If it wasn't taken "out" of service (such as a disposition or conversion to personal use), it is still "in" service. 

I don't know where the 'official' information about idle property is, but the easy-to-read version is Publication 946:

Idle Property

Continue to claim a deduction for depreciation on property used in your business or for the production of income even if it is temporarily idle (not in use). For example, if you stop using a machine because there is a temporary lack of a market for a product made with that machine, continue to deduct depreciation on the machine.

https://www.irs.gov/publications/p946#en_US_2020_publink1000107334