DES MOINES, Iowa — An Iowa judge has ruled that the details of “shadow insurance” subsidiaries created by several life insurers can remain confidential.

Indiana University professor emeritus Joseph Belth sought the documents last year under Iowa’s open records law, saying he believes they would expose risky financial practices that could bankrupt some insurers.

Judge Lawrence McLellan sided Thursday with the industry and state regulators, saying the documents are part of the companies’ “plans of operations” and exempt from disclosure.

Companies such as TransAmerica have taken advantage of an Iowa law to transfer billions of dollars in liabilities to subsidiaries. Insurers say the arrangements free them from accounting rules mandating that they hold excess cash reserves.

Belth is seeking copies of the financial guarantees the companies made to their subsidiaries, saying policyholders and shareholders should know whether they’re sound.