Since its creation in 1991, id Software has been an independent game, and a fairly heavy hitter within the Dallas Gaming Mafia. Robert Altman, CEO of ZeniMax, says, "Our intention is to make sure id Software will continue to do what they do best – make AAA games." That said, the publishing deal won't affect Rage, which is still being published by (now) rival company Electronic Arts.
No monetary details were released however it can be assumed that it wasn't for peanuts. Todd Hollenshead, CEO of id says, "We will now have financial and business resources to support the future growth of id Software, a huge advantage which will result in more and even better games for our fans." Most the higher ups and people integral to id have signed long term contracts, so hopefully there won't be a large contingent switching teams after the purchase.