DES MOINES, Iowa (AP) — Jeb Bush is releasing a third of a century of his personal income tax returns, a record disclosure for presidential candidates.

The returns Bush planned to release late Tuesday were to include the eight years since he left office as Florida governor, a period during which he served on numerous corporate boards and saw his income rise sharply.

Presidential contenders are required to file financial disclosure forms within 30 days of announcing their candidacy. But those records reflect only sources of income, transactions, assets and liabilities, and the same information for their spouses. The figures are also categorized in ranges, such as $5 million to $25 million.

Tax returns are much more detailed, and it has become customary in the past several decades for presidential candidates to make them public.

"At this point, it's a political requirement, if not a legal one," said Joseph Thorndike, director of the Tax History Project, a group that has collected tax forms for presidents and top presidential candidates since 1995.

But no candidate has released as many returns as Bush planned to. The closest was Bob Dole, the 1996 Republican nominee, who released 29 years of his income tax returns. In 2004, Democratic nominee John Kerry disclosed 20 years of such records.

The 2012 Republican nominee, Mitt Romney, was hammered by critics for refusing to release more than two years of his tax returns. Romney instead released a letter from his tax advisers offering a summary of his tax liability for a 20-year period. Among other things, the letter described his charitable giving and the range of his effective federal tax rates.

Bush is the first of the nearly two dozen major candidates for president in 2016 to release tax returns. But Ron Weiser, a former finance chairman at the Republican National Committee, said Bush's actions are aimed not at his competition for the GOP nomination but at Democratic front-runner Hillary Rodham Clinton.

"What Bush reports having made is likely much less than what Hillary Clinton has made, and she's portraying herself as for the little guy," Weiser said.

Bush's rivals did not indicate when their tax returns might be made public. Marco Rubio's team, for one, said his returns will come out but declined to say when.

Clinton has filed the financial disclosure form required by the Federal Election Commission but has not made public her tax returns.

Bush's returns were likely to show how his net worth increased dramatically after he completed two terms as Florida governor in 2007.

He left office less wealthy than when elected in 1998. The decline in his net worth, from $2 million in 1998 to less than $1.3 million in early 2007, came largely from a diminished investment portfolio, according to previously released financial disclosures.

Bush also earned less as governor — $129,000 his last year in office — than he did in the private sector, where he had been paid $755,000 annually by a development company in Coral Gables, Florida, before taking office.

Since leaving the public sector, Bush has served on the boards or as an adviser to at least 15 companies and nonprofits, earning at least $3.9 million from four companies alone since 2007. His tax returns are likely to fill in details from his service on the boards.

Bush previously released some tax returns when he ran for Florida governor, so the batch of 33 will include some already made public.

His 1998 tax return, for instance, the last before he became governor, listed total income of $782,607 — nearly all from his pay at the Codina Group in Coral Gables.

The earlier tax returns also detail Bush's foray into real estate and other businesses, pro football among them. He owned a stake in the NFL's Jacksonville Jaguars and reported selling his interest July 1, 1997, with 526,531 in income from the sale.

Campaign spokeswoman Allie Brandenburger says Bush's decision to release the tax returns "is consistent with the high level of disclosure he has practiced during his life in public office."

In February, Bush released more than 275,000 emails that were sent to and from his private email account during his time as governor.

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Greene reported from Washington. Associated Press writer Julie Bykowicz contributed from Washington.