Participants enrolled in the study prior to Amendment 3 were randomized in a 1:1 ratio to receive adalimumab or placebo during the 12-week DB induction period. Participants received 4 injections of adalimumab 40 mg (160 mg) or 4 injections of placebo at Baseline (Week 0), followed by 2 injections of adalimumab 40 mg (80 mg) or 2 injections of placebo at Week 2, followed by 1 injection of adalimumab 40 mg or placebo at Weeks 4 and 6. At Week 8, participants randomized to placebo received 4 injections of adalimumab 40 mg (160 mg) followed by 2 injections of adalimumab 40 mg (80 mg) at Week 10. Participants randomized to adalimumab received 3 injections of placebo and 1 injection of adalimumab 40 mg at Week 8 and 1 injection of placebo and 1 injection of adalimumab 40 mg at Week 10. All participants continued to receive 1 injection of open-label (OL) adalimumab 40 mg every other week beginning at Week 12 up to Week 52 (or the early termination visit). Starting at Week 14, participants who had inadequate responses to treatment (as defined using partial Mayo scores) were permitted to dose escalate to adalimumab 40 mg weekly. Participants with persistent inadequate response while on weekly treatment could be discontinued from the study at the discretion of the investigator.