WP Engine, one of the largest hosting companies that specialize in running WordPress sites, today announced that it has raised $15 million in funding from North Bridge Growth Equity. The company says the funding is meant to help it accelerate growth and invest in product innovation across its platform.

This latest round of funding, the company’s CEO Heather Brunner told me earlier this week, brings the company’s total funding to $18.2 million. According to Brunner, WP Engine still had a good amount of its earlier funding in the bank, but decided to go ahead and raise now in order to be able to grow its service quickly. While the company has about 100 employees right now, Brunner expects to double this number by the end of the year. Come 2015, WP Engine also plans to open its first international office in Europe. Today, WP Engine has offices in Austin and San Francisco.

The company, Brunner told me, has grown about 25 percent every quarter since inception and currently has about 14,000 customers who host over 120,000 unique sites and domains on its platform. Those sites pay host to about 36 million unique visitors per day. According to the company’s own data, it posted 3x year-over-year revenue growth last year and expects to double revenue this year.

Because of this rapid growth, WP Engine received a lot of inbound interest from venture capital firms. After looking at about 20 offers, Brunner said, the company decided on North Bridge. The executive team was mostly interested in finding a good fit between the VC and WP Engine.

North Bridge fit the bill because its portfolio includes a number of companies with open source backgrounds. As part of this funding deal, the company has added Matthew Blodgett, a general partner at North Bridge Growth Equity, to its board. Blodgett, Brunner told me, will especially be able to help the company optimize its growth strategy.

WP Engine isn’t planning on using any of the new funding for acquisitions, though it did just announce a very small one. The company took over the hosting business of Crowd Favorite last week, though this was more of a user acquisition deal than an exchange of employees and technologies.

Looking ahead, WP Engine plans to build a number of new tools for its customers and bring some it currently uses internally to its users as well, though Brunner didn’t go into any details about which tools it has planned. She did say, however, that the company plans to continue to focus on making WordPress faster, more scalable and more secure.