According to court documents obtained by PEOPLE, the Academy Award winner, 47, listed “irreconcilable differences” as the reason for their divorce when she filed Saturday in the Circuit Court of Davidson County, Tenn.

Witherspoon’s document lists the filing date as the date of their separation and says the couple has a pre-nuptial agreement in place. She also asks the court to designate her and Toth as joint custodians of their 10-year-old son, Tennessee James.

Witherspoon and the CAA talent agent announced their divorce in a joint statement last Friday, days before their 12th anniversary.

“We have some personal news to share…” they began. “It is with a great deal of care and consideration that we have made the difficult decision to divorce. We have enjoyed so many wonderful years together and are moving forward with deep love, kindness and mutual respect for everything we have created together.

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“Our biggest priority is our son and our entire family as we navigate this next chapter. These matters are never easy and are extremely personal. We truly appreciate everyone’s respect for our family’s privacy at this time,” the pair added.

A source told PEOPLE that the two “really are the best of friends,” adding: “This is such an amicable decision. They are so committed to co-parenting together. They are invested in their whole family and making this as smooth as possible for everyone.”

Another insider said that Witherspoon is “headstrong and focused,” while Toth is the more “laid-back” one in their relationship. “They’ve been spending less and less time together while she was working,” the source said.

Witherspoon and Toth tied the knot in March 2011. In addition to Tennessee, she and ex-husband Ryan Phillippe also share daughter Ava Elizabeth, 23, and son Deacon Reese, 19.