Nah the $18M is probably mostly signing bonus ($12M I'm guessing?) and the rest would be salary and a roster bonus probably.
If I guessed correctly his 2012 cap number would be $8-9M. $3M in prorated SB and $6M between base salary and bonuses. If the bonuses are incentive based they're probably not that much (like probably $1M or so of the $6M).