Benefit plans	12 Months Ended
Dec. 31, 2012
Benefit plans [Abstract]
Compensation and Employee Benefit Plans [Text Block]	Benefit plans 401(k) plan The Company maintains a defined contribution 401(k) plan, which covers all employees who meet certain age and length of service requirements. Plan participants can elect to defer pre-tax compensation through payroll deductions. These deferrals are regulated under Section 401(k) of the Internal Revenue Code. The Company matches 50% of eligible participants’ deferrals that do not exceed 4% of their pay (subject to limitations imposed by the Internal Revenue Code). The Company’s matching contributions were $1.8 million, $1.8 million and $2.1 million for the years ended December 31, 2012, 2011 and 2010, respectively. Neither the 401(k) plan nor any other Company benefit plan holds or invests in shares of the Company’s common stock or derivative securities based on the Company’s common stock. Health benefit plan The Company maintains a qualified health benefit plan for active, full-time employees, which is self-funded by the Company with respect to claims up to a certain amount. The plan requires contributions from eligible employees and their dependents. The Company’s contribution expense for the plan was approximately $30.4 million, $28.3 million and $32.0 million for the years ended December 31, 2012, 2011 and 2010, respectively. At December 31, 2012, estimated liabilities for unpaid and incurred but not reported claims totaled $3.1 million, compared to $3.4 million at December 31, 2011. Deferred compensation plan In 2001, the Company adopted a non-qualified deferred compensation plan for certain highly compensated employees, which was amended and restated effective January 1, 2008. With respect to amounts earned through the year ended December 31, 2011, the Company matched, on a dollar-for-dollar basis, up to the first 5% of participants’ annual salary deferrals and the first 5% of participants’ annual bonus deferrals in each participant’s account. Matching contributions by the Company for the years ended December 31, 2012, 2011 and 2010 were $0.1 million, $1.3 million and $1.2 million, respectively. Effective December 31, 2011, ACI’s Board of Directors terminated the deferred compensation plan. As of December 31, 2012 and 2011, plan assets were zero and $15.3 million, respectively, and are reflected in prepaid expenses and other current assets in the 2011 presentation. The liabilities due the participants were zero and $12.8 million as of December 31, 2012 and 2011, respectively. In 2011, the liability balance is reflected in accrued liabilities in the accompanying consolidated balance sheets. For the years ended December 31, 2012, 2011 and 2010, net deferred compensation expense was $1.2 million, $2.1 million and $1.4 million, respectively.

Benefit plans

401(k) plan

The Company maintains a defined contribution 401(k) plan, which covers all employees who meet certain age and length of service requirements. Plan participants can elect to defer pre-tax compensation through payroll deductions. These deferrals are regulated under Section 401(k) of the Internal Revenue Code. The Company matches 50% of eligible participants’ deferrals that do not exceed 4% of their pay (subject to limitations imposed by the Internal Revenue Code). The Company’s matching contributions were $1.8 million, $1.8 million and $2.1 million for the years ended December 31, 2012, 2011 and 2010, respectively. Neither the 401(k) plan nor any other Company benefit plan holds or invests in shares of the Company’s common stock or derivative securities based on the Company’s common stock.

Health benefit plan

The Company maintains a qualified health benefit plan for active, full-time employees, which is self-funded by the Company with respect to claims up to a certain amount. The plan requires contributions from eligible employees and their dependents. The Company’s contribution expense for the plan was approximately $30.4 million, $28.3 million and $32.0 million for the years ended December 31, 2012, 2011 and 2010, respectively. At December 31, 2012, estimated liabilities for unpaid and incurred but not reported claims totaled $3.1 million, compared to $3.4 million at December 31, 2011.

Deferred compensation plan

In 2001, the Company adopted a non-qualified deferred compensation plan for certain highly compensated employees, which was amended and restated effective January 1, 2008. With respect to amounts earned through the year ended December 31, 2011, the Company matched, on a dollar-for-dollar basis, up to the first 5% of participants’ annual salary deferrals and the first 5% of participants’ annual bonus deferrals in each participant’s account. Matching contributions by the Company for the years ended December 31, 2012, 2011 and 2010 were $0.1 million, $1.3 million and $1.2 million, respectively.

Effective December 31, 2011, ACI’s Board of Directors terminated the deferred compensation plan. As of December 31, 2012 and 2011, plan assets were zero and $15.3 million, respectively, and are reflected in prepaid expenses and other current assets in the 2011 presentation. The liabilities due the participants were zero and $12.8 million as of December 31, 2012 and 2011, respectively. In 2011, the liability balance is reflected in accrued liabilities in the accompanying consolidated balance sheets. For the years ended December 31, 2012, 2011 and 2010, net deferred compensation expense was $1.2 million, $2.1 million and $1.4 million, respectively.