Video game publisher Paradox Interactive just had its “best year to date,” CEO Ebba Ljungerud said during a financial results report on Tuesday.

The company had its best income quarter in Q4 2018, despite not releasing any new games during that time. Revenues increased 51% to 336.9 million SEK (about $36 million USD) compared to Q4 2017. Operating profit rose 69% to 146.8 million SEK ($15.8 million USD).

Five Paradox Interactive titles were mainly responsible for fourth quarter revenue growth — “Cities: Skylines,” “Stellaris,” “Crusader Kings II,” “Europa Universalis IV,” and “Hearts of Iron IV.”

Meanwhile, revenues for the year were up 39% to 1.1 billion SEK ($118 million USD) compared to the same time period last year, and operating income increased 34% to 455 million SEK ($49 million USD).

Ljungerud believes the publisher’s success during the fourth quarter demonstrates the strength of its core strategy to develop and support games and brands in the long term. The company released 16 new expansions throughout 2018. Six of them launched during the fourth quarter — Industries for “Cities: Skylines,” MegaCorp for “Stellaris,” Flashpoint for “Battletech,” Space Race for “Surviving Mars,” Holy Fury for “Crusader Kings II,” and Golden Century for “Europa Universalis IV.”

“Continuous updates and expansions give our games a long life, both in terms of number of players and recurring revenue,” she said.

Paradox also made a number of acquisitions in 2018. It picked up “Battletech” creator Harebrained Schemes and now has a minority stake in Hardsuit Labs, which is working on an unannounced title. It ended the year by announcing the acquisition of the “Prison Architect” rights and assets from Introversion Software. The construction and management sim is currently available on PC, Mac, Linux, consoles, and mobile, and it’s sold over two million copies since 2015.

“Through the acquisition of ‘Prison Architect,’ we are laying an important building block for future growth within the management genre, where ‘Cities: Skylines’ and ‘Surviving Mars’ are currently our most successful games,” Ljungerud said. “Constantly adding new games and brands to our portfolio remains a core part of our strategy. It helps ensure longevity and lessens our dependency on all releases being hugely successful from day one.”

Paradox is adding two completely new games to its portfolio in 2019 — “Age of Wonders: Planetfall” and “Imperator: Rome.” It will also reveal more information about some unannounced projects, and introduce console gamers to the grand strategy genre via “Stellaris: Console Edition,” which launches in early 2019.