(Reuters) – Aon Plc bounced back from a weak first quarter to post an estimate-topping profit as investments in its human resources business begin to pay off despite lingering margin concerns.

Shares of the company rose as much as 6 percent, their biggest single-day percentage gain in more than 4 years, to $49.33 in morning trade on Friday on the New York Stock Exchange.

The company no longer expects operating margins in the HR business to fall in the third quarter and expects a modest rise in the fourth quarter.

“While macro conditions remain fragile globally, we continue to anticipate improved performance in the second half of the year,” Chief Executive Greg Case said in a statement.

The company operates under two main segments – risk solutions and HR solutions. The risk solutions unit includes Aon’s retail insurance brokerage and reinsurance business, while the HR solutions unit consists of consulting and outsourcing operations.

Costs at the company’s HR segment have been rising due to investments in healthcare exchanges and HR business process outsourcing, and have been a major reason for the squeeze on margins in the last few quarters.

In May, it reported its first fall in quarterly profit after three quarters of year-over-year profit increases, hurt by lower margins at its HR segment, Aon Hewitt.

However, the management has been consistent in its view that these capital-light investments would start to pay off towards the beginning of 2013.

For the second quarter, operating costs at the HR segment rose 8 percent and operating margins fell to 15.4 percent on an adjusted basis, the company said.

The company’s long-term targets include operating margins of 22 percent in HR solutions and 26 percent in risk solutions. 

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Net income from continuing operations fell 4 percent to $247 million, or 73 cents per share, from $256 million, or 75 cents per share, a year earlier.

Excluding items, the company posted earnings of $1.02 per share from continuing operations.

Total revenue for the quarter increased marginally to $2.81 billion, helped by a 4 percent organic growth in both its risk solutions and human resources solutions units in the quarter.

Analysts on average were expecting Aon to earn $1.01 per share, on revenue of $2.89 billion, according to Thomson Reuters I/B/E/S.

Aon, which competes with Marsh & McLennan Co. and Willis Group Holdings in negotiating insurance and reinsurance policies for corporate clients, said it is on track to meet its long-term targets.

Shares of the company, which has a market capitalization of $15.1 billion, have fallen 10 percent in the past three months, underperforming the broader S&P 500 Index, which has fallen about 7 percent during the period.