Idaho voters turned out in record numbers Tuesday night to deliver a victory for Barack Obama in the Democratic caucuses.

Obama, a first-term U.S. senator from Illinois, trounced Sen. Hillary Clinton of New York, winning in 34 of the 35 counties that reported results by the time the race was called by The Associated Press.

Idaho, with 18 delegates at stake in the race for the Democratic presidential nomination, was a state that Obama's campaign targeted last fall, then sought to lock down with his standing-room-only campaign rally last weekend in Boise.

Under party rules, delegates will be awarded proportionally based on total vote in each of the state's two congressional districts.

Obama's victory came as the party set new marks for caucus turnout. Some would-be voters weren't even able to squeeze into the 6,800-seat Qwest Arena in downtown Boise, site of the Ada County caucus.

"To be a Democrat in Idaho has always been the right thing to do, but tonight it's the cool thing to do," state party Chairman Keith Roark told voters.

Four years ago, just 2,000 people attended the Democratic caucus in Ada County, Idaho's most populous. Across the state, just 4,920 participated in 2004.

Party officials said late Tuesday they had not yet tabulated total turnout. But John Foster, the party's executive director, said unofficial counts showed turnout had doubled 2004 totals even before the party included the state's biggest counties, including Ada, Bannock and Canyon.

Democratic party leaders anticipated a night of heavy turnout, thanks to enthusiasm for candidates Obama and Clinton and moving the caucus from March to be a part of Super Tuesday.

Still, they were caught off guard by the number of people who wanted to participate in Ada County. Earlier in the day, organizers printed 9,000 ballots to hand out to overflow crowds, then printed more just to make certain they didn't run out. Altogether, 8,290 ballots were counted, according to the Ada County Democratic Party's final count.

For some of the caucus-goers, the ballots were their only chance to participate. Once Qwest Arena reached capacity, party officials would not let anyone else inside, instead simply collecting ballots from those left outside.

Last Saturday's Obama rally boosted interest in the caucuses, attracting more than 14,000 people to Boise State University's basketball arena.

Nick Bayus of Boise said the enthusiasm by Democrats outweighed any irritation at being turned away from the arena.

"I'm just thrilled there are so many people here, so many Democrats," Bayus said.

Organizers had expected record caucus turnout across the state as Democrats in mostly Republican Idaho sought to make their voices heard in the race to replace President George Bush. Still, all the congressional seats and statewide elected positions in Idaho remain in GOP hands.

"I want to get as far away from Bush as you can get," said David Walgren, a Boise Democrat who supports Obama. "Obama is as far away from Bush as you can get."

Unlike other states that caucus by precinct, Idaho Democrats had just a single caucus site per county.

In addition to the Democratic delegates selected Tuesday, Idaho also has five "superdelegates" -- consisting of elected or party officials who aren't bound to endorse a candidate based on caucus results. Instead, the superdelegates can vote their will at the Democratic National Convention in Denver in late August.

Idaho Republicans will vote in their primary May 27.