Danish to English Art/Literary Poetry & Literature

This is an excerpt from a letter written in the end of the nineteenth century; the writer is talking about a person who seems to be sloppy, actually the context is provided by the previous sentence, that I translated as follow: “He doesn’t give importance to things, he takes care of the small everyday concerns no more than of matters of the greatest importance.”
Although the general meaning is quite clear, I have some problem in translating “han har sit liggende fæ i himmelen”. I guess that it is an idiomatic expression, but I don’t know it in Danish.

Thanks.