White House hopeful Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE on Thursday released his tax returns from 2009 to 2017, confirming the former hedge fund manager's significant income.

Steyer and his wife, Kat Taylor, filing jointly, made $146.3 million in adjusted gross income in 2017 and paid total federal taxes of $32.5 million, easily making him the biggest earner among the crowded field of Democrats running for president.

The couple's adjusted gross income in 2017 was higher than it was the preceding year, when the two made $80.4 million.

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In 2012, Steyer's final year as the head of investment firm Farallon Capital Management, he and his wife made $174.3 million.

The couple has signed the Giving Pledge, a commitment from billionaires to donate a significant portion of their wealth.

The campaign also said that Steyer ramped up his political involvement in the past decade.

In 2009, the couple gave $52,500 to political activities. In 2016, that number surged to $139.6 million.

In 2017, a non-election year, the couple gave $65.4 million to political activities, according to the memo from Steyer's campaign.

Many of the other Democratic presidential candidates released their tax returns earlier this year.

Before Steyer's disclosure, former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE's reported income of $15.6 million in 2017 and 2018 was the biggest among prominent 2020 candidates including Sens. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) and Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.).

Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.) and her husband reported the next highest income in 2018, at just under $1.9 million.

Democrats have been releasing their returns in an effort to argue that they are more transparent than President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE. In 2016, the president became the first major-party nominee to refuse to make his tax returns public.

Steyer has used his personal wealth to funnel more than $10 million into digital and television advertisements since entering the race in July.

Although that investment helped get him to the 130,000 individual donor threshold needed to qualify for the third and fourth Democratic primary debates, he was one qualifying poll short of making it to the Democratic primary debate stage on Sept. 12.

Steyer still has a chance to qualify for the fourth debate in October.