ACA and its anticipation
A lot of the increase can be attributed to the ACA and it anticipated effects. Employers now have to pay for children up to age 26, for example. The areas of health care that have to be covered has also been widened. That costs. It's why well over a thousand self-insured companies asked for and were granted temporary waivers from parts of the ACA that are already in effect.
Most health insurance companies also anticipate that in 2014 when the ACA fully kicks in, health care premium increases will be completely controlled by the government. To be perfectly blunt, they're raising premiums while they can.
To quote the summary report referred to in the article, "The 9% growth rate in family premiums for 2011 is significantly higher than the 3% growth rate in 2010." That's mainly because of the ACA and its anticipated effects.
