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bonuses and sales commissions, contributed approximately two- thirds of the overall operating expense increase in this segment. Bonus expense rose $4.2 million in 2010. Sales commissions and employee benefits, including employee healthcare benefits and matching contributions to our 401(k) plan in the United States, also increased, but to a lesser extent. Operating expense in 2010 also includes $2.0 million related to a separation agreement between Morningstar and the former head of Morningstar Associates. A slight reduction in product implementation fees related to our Advice by Ibbotson service partially offset these increases. 

In 2009, the operating expense decrease was primarily because of lower bonus and other compensation-related expense, partially offset by additional operating expense related to the Intech acqui- sition. Bonus expense declined $10.4 million in 2009. Most of this reduction reflects the changes we made to our bonus program for 2009 as part of our efforts to better align our cost structure with revenue. The reduction in bonus expense also reflects a slowdown in our financial performance in 2009 compared with 2008. Other compensation-related expense was down, primarily because we suspended matching contributions to our 401(k) plan in the United States, reducing operating expense by $1.3 million in 2009. A slight reduction in product implementation fees related to our Advice by Ibbotson service also contributed to the decrease. 

The segment’s operating margin in the segment decreased 5.8 per- centage points to 51.5% in 2010. The margin decline mainly reflects higher bonus expense as a percentage of revenue. The $2.0 million separation payment reduced the margin by approximately 2.0 per- centage points. Salaries and employee benefits also contributed to the margin decline, but to a lesser extent. In addition, acquisitions had a negative impact on the margin of approximately 1.6 percent- age points. 

Operating margin was 57.3% in 2009, an increase of 3.3 percentage points over 2008. Lower bonus expense as a percentage of revenue was the main driver of the margin improvement. The decrease in other compensation-related expense also contributed to the margin improvement, although to a much lesser extent. These factors were offset by incremental costs from the Intech acquisition and higher compensation expense as a percentage of revenue. 

## Corporate Items 

We do not allocate corporate costs to our business segments. The corporate items category also includes amortization expense related to intangible assets recorded when we allocate the purchase price of acquisitions. The table below shows the components of corporate items that impacted our consolidated operating income: 

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Amortization of intangible assets increased $5.9 million in 2010 and $2.4 million in 2009, mainly reflecting incremental amortization expense related to acquisitions completed in 2010 and 2009. We paid $281.9 million for acquisitions during the past three years. As of December 31, 2010 and December 31, 2009, respectively, we had $169.0 million and $135.5 million of net intangible assets. We amor- tize these intangible assets over their estimated lives, ranging from one to 25 years. Based on acquisitions completed through December 31, 2010, we estimate that aggregate amortization expense for intangible assets will be approximately $25.7 million in 2011. Some of the purchase price allocations are preliminary, and the values assigned to intangible assets and the associated amortization expense may change in future periods. 

After increasing $3.5 million in 2009, depreciation expense for cor- porate departments did not change significantly in 2010 from 2009. We relocated to our new corporate headquarters in the fourth quar- ter of 2008, resulting in higher depreciation expense in the subse- quent years. 

In 2010, corporate unallocated expense decreased $8.9 million, as some expenses recorded in 2009 did not recur in 2010. Corporate unallocated expense in 2009 includes $9.5 million of expense related to adjusting the tax treatment of certain stock options and deposit penalties. In 2010, expense related to liabilities for vacant office space declined $2.2 million. In addition, in 2010 we capitalized approximately $0.8 million of operating expense for software devel- opment. These factors, which favorably impact the year-over-year comparison, were partially offset by incremental expense from acquisitions, higher compensation and bonus expense, and higher professional fees. 

