Of the 20 leading U.S. excess and surplus insurers, 15 posted double-digit year-over-year growth in direct premiums written during the first quarter, according to an S&P Global Market Intelligence analysis.

Markel Corp. supplanted Berkshire Hathaway Inc. in the No. 2 spot after its direct premiums written soared 39.9% to $799.8 million from $571.5 million in the first quarter of 2020. Berkshire's direct premiums written went up 21.3% to $758.9 million from $625.8 million a year earlier, landing it in the third spot.

American International Group Inc. holds a slim lead at the top, as its direct premiums written ticked up 4.9% from the prior-year period to $818.0 million.

Broker Ryan Specialty, which placed 70.6% of its total premiums in the E&S market in 2020, said in an IPO filing that the "emergence of complex, unique or otherwise hard-to-place risks," as well as the need for specialist solutions, has driven meaningful growth within what it described as the "increasingly important" U.S. E&S market.

Citing A.M. Best data, Ryan Specialty noted that E&S grew at a faster rate than the U.S. admitted market between 2010 and 2019. E&S market share as a percentage of total U.S. commercial insurance premium increased to 16.9% in 2019 from 14.2% in 2010, the broker said.

Ryan Specialty added that a "shift towards complex risks" will insulate the E&S market from broader economic trends. It cited wildfires, escalating jury verdicts and social inflation, cyber threats and novel health risks as examples of complex risk.

Overall, the U.S. E&S market saw direct premiums written jump by 25.4% on a yearly basis to $12.93 billion in the first quarter.