At length
Definition 1 of 2
Pro Tip 1/3Extended Talk
Use 'at length' when someone talks or writes more than usual about a subject. 
The professor spoke at length about climate change.
Pro Tip 2/3Deep Dive
'At length' indicates going into great detail about a complex or important issue. 
She described her research findings at length in her presentation.
Pro Tip 3/3Extended Writing
In writing, 'at length' suggests a thorough examination or elaboration on a topic. 
In his book, he examines the history of Rome at length.