Arch also reported Monday that its combined ratio for the first nine months was 92.4%, up from last year's nine-month combined ratio of 88%.
Meanwhile, the Hamilton, Bermuda-based insurer said it had $2.6 billion in gross written premiums during the first nine months of this year, down slightly from last year's $2.8 billion.
For the third quarter, Arch reported that its net income was down 48% to $141.6 million, compared with 2009's third-quarter results. The sharp drop could be attributed to the weak foreign exchange rate for the U.S. dollar, which created a $65.3 million loss for the insurer.