Koch Brothers' Super PAC 's 20 Donors Contributed This Much

David Koch, executive vice president of Koch Industries, attends an Economic Club of New York event in New York
David Koch, executive vice president of Koch Industries, attends an Economic Club of New York event in New York, December 10, 2012. RBrendan McDermid / REUTERS file

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By Leigh Ann Caldwell

INDIAN WELLS, CALIFORNIA -- The Koch brothers' super PAC raised $11 million in the second half of 2015, according to documents filed with the Federal Election Committee, bringing the group's total cash on hand to $14.8 million.

Only 20 donors contributed the $11 million. Half of the money came from Charles Koch and two others.

While the group brought in a significant amount of money, it spent little. Freedom Partners Action Fund, which must disclose the donors and amount given, spent just over $200,000 since June and only $260,000 in 2015.

The Koch network has stayed out of presidential politics so far and its only political activity has been in four Senate races - Ohio, New Hampshire, Pennsylvania and Nevada - opposing the Democratic candidate. The modest $260,000 spent was mostly for legal fees, bookkeeping, credit card fees and grants to its partner organization, Freedom Partners Chamber of Commerce.

Still, the organization received large donations, including $2 million from hedge fund manager Kenneth Griffin, who also gave $2.5 million to the super PAC Conservative Solutions backing Sen. Marco Rubio for president.

Diane Hendricks of Wisconsin and a major supporter of Governor Scott Walker gave $2 million.

Charles Koch gave $3 million to his super PAC.

The super PAC spending, however, doesn't tell the story of the Koch's national engagement. The network, overseen by Charles and David Koch, has spent almost thirty times the amount of the super PAC - nearly $400 million in 2015.

The $400 million was spent by a myriad of groups that operate under a component of the tax code that does not require the organization to reveal who their donors are. The groups have been active courting key constituencies, training political candidates, mobilizing volunteers to push policy, giving grants to like-minded groups.

RELATED: Charles Koch: We Are Not 'Some Secret Cabal'

Sunday is the first full day of the biannual Koch donor retreat, which is called the "seminar." It is taking place at a golf resort near Palm Springs, California.

Organizers say this is the largest conference yet, with 500 participants -- of which one third are in attendance for the first time. A $100,000 entry fee is required to become a member.