Green’s Dictionary of Slang

(US) the whole world, also used fig. to mean a lot; often used as a general intensifier, as in big as all outdoors, tall as all outdoors.

1825		J. Neal Brother Jonathan I 111: Stuffy feller (that bear) as ever you see’d; big as all out o’doors.
1830		S. Smith Life J. Downing 64: I had a letter from him t’other day, as long as all out doors, in the Boston Advertiser [DA].
1840		T. Haliburton Clockmaker III 78: He lathers his chin with an English brush and English soap, a-lookin’ as big as all out doors.
1848		J.R. Lowell Biglow Papers (1880) 114: It takes a mind like Dannel’s, fact, ez big ez all ou’ doors.
1860		T. Haliburton Season Ticket 12: It’s as big as all out-doors, and you know how big that is.
1884		C.F. Lummis letter 1 Dec. in Byrkit Letters from the Southwest (1989) 126: The roof serving as floor to a sky-thatched attic as big as all outdoors.
1892		in Punch 3 Dec. 258: He looks as big as all out-of-doors.
1903		G.D. Chase ‘Cape Cod Dialect’ in DN II:v 302: The following miscellaneous expressions are also noticeable [...] big as all out doors.
1907		W.M. Raine Wyoming (1908) 61: ‘And if I don’t agree with y’u?’ ‘There’s all outdoors ready to receive y’u, seh.’.
1918		R.D. Paine Fighting Fleets 196: This veritable porpoise of a sea-cook with a soul as big as all outdoors.
1918		R.H. Knyvett ‘Over There’ with the Australians 6: What healthy youngster, with ‘all out-of-doors’ around him, would study by himself?
1926		in J.F. Dobie Rainbow in Morning 90: As big as all outdoors.
1948		Chicago Trib. 28 Mar. IV 6/3: Its spirit is literally ‘as big as all out-doors’ [DA].
1962		P. Crump Burn, Killer, Burn! 273: My heart is as big as all outdoors where you’re concerned.
1977		R. Coover Public Burning (1979) 412: What a wind! It come rippin’ hell’s bells outa the north as big as all outadoors.
1994		G. Indiana Rent Boy 107: ‘Fuck, Mavis, you know I’ve got a major heart.’ ‘Mmm-hmm, big as all outdoors.’.