Centene Corp. (CNC) has operated against the trend in the last couple of years.

The health insurer announced plans in July 2015 to buy Health Net Inc. for $6.8 billion, just as two bigger rivals tried for megadeals of their own. Centene's deal was quickly blessed by the Department of Justice while Anthem Inc.'s (ANTM) plan to acquire Cigna Corp. (CI) and Aetna Inc.'s (AET) bid for Humana Inc. (HUM) , unveiled within weeks of Centene's offer, were challenged by the DOJ and ultimately blocked in federal court.

Now, as major insurers are exiting Obamacare exchanges, Centene is expanding its commitment to offering policies under the Affordable Care Act.

Centene said Wednesday that it will expand its offerings in the 2018 Health Insurance Marketplace, the formal name for the Obamacare exchanges by entering Kansas, Missouri and Nevada in 2018. Centene said it will also expand its footprint in six existing markets: Florida, Georgia, Indiana, Ohio, Texas, and Washington.

Centene's added commitment to the ACA exchanges runs counter to the actions of most other insurers, which have imposed double-digit premium increases or left exchanges altogether due to costs of maintaining a program where no one with pre-existing conditions can be denied coverage.

Anthem pulled out of Ohio's individual insurance exchange in early June, citing low enrollment and uncertainty over the fate of federal subsidies necessary to make the policies more affordable for lower income individuals. Anthem's departure would leave 20 Ohio counties with no insurers on Obamacare's exchange, which cover people who don't get plans through their employer or federal programs.

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