Goodwill represents the excess of the purchase price over the estimated fair value of net tangible and identifiable intangible assets acquired in business combinations. Our annual impairment assessment is performed as of October 1 ^st of each year, and an assessment is performed at other times if events or circumstances indicate it is more likely than not that the asset is impaired. At October 1, 2011 and 2010, the fair value of our single reporting unit substantially exceeded its carrying value and therefore was not at risk of failing step one of ASC 350-20, Goodwill (“ASC 350-20”). Subsequent to our annual evaluation of the carrying value of goodwill, there were no events or circumstances that triggered the need for an interim evaluation for impairment. There were no changes in the carrying value of our goodwill during the years ended December 31, 2011, 2010 and 2009.