Shares of Insperity Inc. (NSP - Get Report) surged 19% to close at $131.97 on Monday after the staffing and outsourcing services company beat Wall Street's fourth-quarter earnings expectations.

The Kingwood, Texas-based company reported earnings of $24.7 million, or 59 cents a share, up from $15.6 million, or 36 cents, Adjusted earnings came to 69 cents a share, up 25% from a year ago, and beat analysts' expectations of 65 cents.

Revenue increased 17% to $966.8 million, on an increase in the average number of worksite employees, or WSEEs, beating Wall Street's forecast of $964 million.

For the year, Insperity reported net income increased 60% to $135.4 million, or $3.22 a share, up 60% from a year ago. Adjusted earnings increased 53% to $3.75 a share. Full-year revenue increased 16% to $3.8 billion, on a 14% increase in the average number of WSEEs paid per month over 2017. The growth was primarily driven by an increase in WSEEs paid from new sales on a 16% increase in the average number of trained business performance advisors.

"As a result of our successful fall selling and retention campaign, we are starting 2019 with 15% worksite employee growth and are well positioned to continue our strong financial performance," Paul J. Sarvadi, chairman and CEO, said in a statement.

Looking ahead, Insperity said it expects first-quarter earnings of $71 million to $74 million, and adjusted earnings of $1.85 to $1.91 a share. For the full year, the company said it expects earnings of $4.37 to $4.69 a share.