does postgreSQL waits for some time before releasing idle connection?

I'm using **CKAN 2.7.2 (docker)** application.
```
max_connection = 200 (postgresql)
queuepool = 15 (Sqlalchemy)-> pool_size=5 && max_overflow=10
Ckan_default processes: 4 (ckan)
```
In my psql's pg_stat_activity table connection details are (```select * from pg_stat_activity;```):

ckandb connections : total 80 connections where active - 51, idle - 20, idle_in_transaction - 09.
ckan_datastore con : total 24 connections where active - 04, idle - 19, idle_in_transaction - 01.

We can see many connections are in `Idle` state.

Does these `Idle` connections are reusable (waiting to serve new request) or these connections are about to release(waiting for release)?

Does postgreSQL takes some time to release the idle connections?(I mean, If there are some idle connections present then, does postgreSQL waits for some time before releasing those idle connection? )