|Idlewild, the summer cottage of the influential Victorian-era Philadelphia architect Frank Furness, is significant under Criterion C, as it is a strong example of a late 19th century Queen Anne/Shingle style residence, and an important part of Furness' body of work. He designed it for his own family's use as a summer residence. It was seasonally occupied by Furness and his family from 1888, when it was built, at least until Furness' death in 1912. He passed away while summering there. It is one of the very few remaining Furness-designed summer dwellings in the Philadelphia area, and the only one of its type in its immediate suburban area. The house's design is important for multiple reasons: it comprises a residential-scale version of one of the most important remaining large buildings in Furness' oeuvre, the University of Pennsylvania's Fisher Fine Arts Library; simultaneously it is a good example of what has been called the understated character of the Furness country houses from the 1870s to the end of his practice [CWFF, p. 321]; and it is an outstanding Fumess-designed representative of the late 19th century Queen Anne style (with hints of Shingle style architecture), the more general version of which was prevalent in the surrounding area at the time. The period of significance is the year of completion, 1888.