arm's length

Short definition from Wiktionary

Noun

1. 1
   A distance approximately equal to the length of a human's arm.
2. 2
   A position not suggesting or inviting intimacy.
3. 3
   A condition of independence and parity for parties to a transaction.

Adjective

1. 1
   Barely within reach.
2. 2
   Distant, detached.
3. 3
   Independent, but related.