According to a recent survey ...

... between 2000 and 2012, employer-sponsored health insurance coverage rates for nonelderly workers fell from 76.9% to 69.4%, and coverage rates fell from 61.1% to 52.4% among workers in small fims (fewer than 50 employees). However, since the implementation of the key coverage provisions of the ACA, between June 2013 and March 2016:

• Offer rates of employer-sponsored health insurance have remained constant at 82-83% for all workers, 61-62% for workers in small firms, and 94% for workers in large firms.
• Take-up rates of mployer-sponsored health insurance remained constant among workers with an employer-sponsored health insurance offer, at about 86 to 87% for all workers, 81-82% for workers in small firms, and 88-89% for workers in large firms.
• Coverage rates of employer-sponsored health insurance also remained constant at 71-72% for all workers, 49-50% for workers in small firms, and 83-84% for workers in large firms.

Source: "Employer-Sponsored Insurance Stays Strong, with No Signs of Decay under the ACA: Findings through March 2016," Health Reform Monitoring Survey, The Urban Institute,July 13, 2016, http://hrms.urban.org/briefs/employer-sponsored-insurance-aca-march-2016.html