Pittsburgh-based health insurer Highmark Inc. has filed 1,600 pages of documents with Delaware's Department of Insurance, formalizing its intention to affiliate with Blue Cross Blue Shield of Delaware, the state's largest health insurance company.

The documents include a statement of affiliation and supporting documents, including Highmark's financial statements.

BCBSD -- which has 320,000 Delaware customers -- and Highmark announced the deal in August.

The deal is subject to approval by state Insurance Commissioner Karen Weldin Stewart. Stewart said she expects to make a decision by March, and that public hearings will be held early next year.

Stewart has appointed a hearing officer -- retired Family Court Judge Battle Robinson -- to scrutinize the deal and offer a recommendation.

"We are particularly looking what dollars swim upstream, and what comes downstream," Stewart said Friday. "That means if money travels upstream to Highmark, is there money coming downstream to Blue Cross and Blue Shield?"

Under terms of the proposed deal, Highmark executives will fill at least three spots on the board of BCBSD. Highmark has said BCBSD will continue to operate independently from its headquarters in Wilmington.

The affiliation agreement says that four board members will remain independent, and will have the authority to terminate the affiliation agreement if certain events occur, including if Highmark converts to a for-profit company, if it becomes insolvent, or if Pennsylvania lawmakers pass legislation that affects the structure of Highmark's board.

That's significant because a similar law passed in Maryland back in 2003 ultimately undermined BCBSD's six-year affiliation with Owings Mills, Md.-based CareFirst Blue Cross Blue Shield.

BCBSD was forced to end that affiliation in 2006 after Insurance Commissioner Matt Denn refused to amend terms of the agreement.

BCBSD has said the deal will give it access to capital improvement money to make upgrades necessary to remain competitive.

It also would be able to tie into systems already in place at Highmark, including claims processing.

BCBSD has been seeking a larger partner since 2006, when it left CareFirst.