The companies also have raked in cash from subsidiaries that provide health care and transportation. And they are holding more immigrants convicted of federal crimes in their privately-run prisons.

The financial boom, which has helped save some of these companies from the brink of bankruptcy, has occurred even though federal officials acknowledge privatization isn't necessarily cheaper.

This seismic shift toward a privatized system happened quietly. While Congress' unsuccessful efforts to overhaul immigration laws drew headlines and sparked massive demonstrations, lawmakers' negotiations to boost detention dollars received far less attention.

The industry's giants — Corrections Corporation of America, The GEO Group, and Management and Training Corp. — have spent at least $45 million combined on campaign donations and lobbyists at the state and federal level in the last decade, the AP found.