Arch Capital Group Ltd bettered the forecast of Wall Street analysts, as it posted $247.4 million of net income for the third quarter.

The Bermuda insurer and reinsurer’s profit represented an annualised return on average common equity of 15.3 per cent.

And Arch grew book value per common share to $53.62 at September 30, a 3 per cent increase from $52.04 per share at June 30 and a 12.5 per cent increase over the past 12 months.

After-tax operating income was $142.5 million, or $1.14 per share, beating the $1.03 consensus forecast of analysts tracked by Yahoo Finance, and up from $125.8 million in the third quarter of 2015.

Arch’s combined ratio — the proportion of premium dollars spent on claims and expenses — improved to 88 per cent from 90.7 per cent in the July through September period last year.

The company wrote more business in the third quarter, with gross written premiums climbing 7.5 per cent to $1.28 billion from $1.19 billion last year.

The major growth driver was Arch’s mortgage segment, which achieved a 76.4 per cent increase in gross premiums to $131.7 million compared to $74.6 million in the prior-year period. Arch said this increase reflected “growth in Australian mortgage reinsurance and in US primary business and from GSE (government-sponsored enterprise) credit risk-sharing transactions receiving insurance accounting treatment”.

Corporate expenses surged to $18.5 million in the third quarter, compared to $10.7 million in 2015. Arch said the increase was primarily due to one-off costs related to the acquisition of United Guaranty Corporation from American International Group. The deal was announced on August 15 this year.