Their second album, "Days of Future Passed", which was released in 1967, was a combination of rock with classical music. This made the band early creators in the development of art rock and progressive rock. It has been described as a "landmark" and "one of the first successful concept albums". The group toured a lot in the early 1970s. Then, they took a long break from 1974 until 1977. Founder Mike Pinder left the group a year after they re-formed. He was replaced by Swiss keyboardist Patrick Moraz in 1978. In the following decade they took on a more synth-pop sound. They created "The Other Side of Life" in 1986. This made them the first band to earn each of its first three top 10 singles in the United States in a different decade. Health problems led to a smaller role for founder Ray Thomas throughout the 1980s. However, he made more music after Moraz left in 1991. Thomas left the band in 2002. The band's most recent album was "December" (2003), a collection of Christmas music. They continued to tour throughout the first decade of the 2000s. They still regroup for some events, one-off concerts, short tours, and cruises.