FARMINGTON, Pa. — Supreme Court Chief Justice John Roberts joked that he'll spend some time on an "impregnable island fortress" now that the court has ended a session that featured him casting the decisive vote to uphold President Obama's health-care law.

Responding to a question about his summer break, Roberts said Friday that he planned to teach a class for two weeks in Malta, the Mediterranean island nation.

"Malta, as you know, is an impregnable island fortress. It seemed like a good idea," Roberts said, drawing laughter from about 300 judges, attorneys and others attending a four-day conference, which started Thursday at the posh Nemacolin Woodlands Resort in Farmington, about 50 miles southeast of Pittsburgh.

Roberts was alluding to escaping criticism from conservatives upset that he sanctioned a law they abhor.

But if the chief justice felt any anxiety about authoring the decision, he didn't show it during the long-scheduled discussion at the biannual Judicial Conference of the District of Columbia Circuit.

Roberts, 57, skirted questions about the health-care ruling and issued a series of quips about everything from his predecessors to rules he would like to change, such as this one: "The odd historical quirk that the chief justice only gets one vote."

Roberts was joined in his decision by the court's four liberal justices: Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan.

His ruling kept in place a major overhaul of the health-care system that is expected to extend coverage to 30 million people.

Roberts' participation in Friday's "Conversation with the Chief Justice of the United States" was scheduled long before anyone knew he would be issuing Thursday's historic ruling.

Chief U.S. District Judge Royce Lamberth and David Sentelle, chief judge of the circuit's appeals court, moderated the discussion.

The closest the session got to the health-care ruling came when Lamberth asked Roberts if it ever bothered the chief justice that he "can't respond to criticism."

"No," Roberts replied, and then pivoted in his chair to face Sentelle for the next question.

The answer provoked widespread laughter in the large conference room.

In response to other questions about the court's work, Roberts described his duty to parcel out opinions to each justice in a way that ensured they all received a variety of cases.

"It's fun. I get a little graph and try to work it out," Roberts said, telling the audience about how he once assigned an opinion and later realized the justice was actually voting "the other way."

"I went and asked him if he could change," Roberts joked.