Idaho Code § 31-2412
It is hereby made the duty of each county recorder in this state, when any instrument, paper or notice authorized by law to be recorded is deposited in the recorder's office for record, immediately to write or stamp thereon an instrument number, and the numbers so stamped shall be consecutive in the order of filing, in only one (1) series of numbers, commencing with the general reception number next in order, upon this amendment becoming effective, in each county and following in the order of the filing of all instruments, papers or notices, and priority of number shall be prima facie evidence of priority of filing: provided, that when such recorder shall receive by mail or other like inclosure more than one (1) instrument, paper or notice at a time, he shall affix such numbers in the consecutive order in which said instruments, papers or notice actually came into his hand on opening, save that when more than one instrument, paper or notice is received from the same source at the same time, he may follow such directions as the sender may give in relation to such numbering. In addition to general reception numbers as above provided the county recorder may use such additional numbers as may be convenient for filing and indexing.
Idaho Code § 31-2412