8. Acquisitions In certain business combinations consummated prior to January 1, 2009, a portion of our purchase price is in the form of contingent consideration. The contingent consideration represents the difference between the seller s and our perceived values of the business based upon our respective future performance estimates at the time of acquisition. The use of contingent consideration allows the buyer to shift some of the valuation risk, inherent at the time of acquisition, to the seller based upon the outcome of future financial targets that the seller contemplates in its valuation. Contingent consideration is payable annually if agreed upon performance targets are met and is generally subject to a maximum amount within a specified time period. Contingent consideration related to acquisitions consummated prior to January 1, 2009 is recorded as additional purchase price with the adjustment recorded as an increase to goodwill if the contingency is satisfied. Additional consideration related to businesses acquired prior to January 1, 2009 that was recorded as an adjustment to goodwill was $18.6 million and $27.3 million for the years ended December 31, 2012 and 2011, respectively. Certain acquisition related restricted stock agreements entered into prior to January 1, 2009 contained stock price guarantees that may result in cash payments in the future if our share price falls below a specified per share market value on the date that the applicable stock restrictions lapse (the  determination date ). For those acquisitions, the future settlement of any contingency related to our common stock price will be recorded as a reduction to additional paid-in capital. During 2012, we paid $4.2 million in cash in relation to the stock price guarantees on certain shares of common stock that became unrestricted, which was recorded as a reduction to additional paid-in capital. Our remaining common stock price guarantees have stock floor prices that range from $54.33 to $69.48 per share and have determination dates thr