Insperity Inc. (NYSE: NSP) reported fourth-quarter revenue rose 4.6 percent year over year to $557.1 million. The Houston-based professional employer organization attributed the rise to a 1.1 percent increase in the average number of worksite employees paid per month and a 3.5 percent increase in revenue per worksite employee per month.

However, gross margin narrowed and net income fell.

Insperity reported fourth quarter net income fell 44.0 percent in the fourth quarter to $5.3 million from $9.4 million in the same quarter last year.

The company reported an after tax non-cash impairment charge of $2.9 million associated with a write-down of goodwill and intangibles related to a 2010 acquisition, partially offset by a $2.0 million tax credit.

Fourth-quarter gross margin narrowed to 16.2 percent from 17.6 percent in the year-ago quarter.

Full-year 2013 revenue rose 4.5 percent to $2.3 billion, while full-year net income fell 20.7 percent to $32.0 million.

Insperity shares fell by 2.35 percent in early afternoon trading to $31.64, according to Yahoo! The company had a market capitalization of $809.03 million.