There are two plays by this name
The Idler by Charles Haddon Chambers (1891)
A play in four acts by Charles Haddon Chambers (1860-1921).
First performed at St James's Theatre, London, on 26 February, 1891.
Published by Samuel French, 1902.
Facsimlie version of the 1902 edition by Samuel French, The Internet Archive
The Idler by Luigi Pirandello (1916)
This is the title given to an English version of Liolà by Luigi Pirandello (1867–1936). Described as a Sicilian comedy, this was Pirandello's first play and opened in 1916.
For more on this play, see the ESAT entry on Liolà