Benefit plans	12 Months Ended
Dec. 31, 2011
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, $2.1 million and $2.2 million for the years ended December 31, 2011, 2010 and 2009, 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 employee health benefit plan that 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 $28.3 million, $32.0 million and $27.3 million for the years ended December 31, 2011, 2010 and 2009, respectively. At December 31, 2011, estimated liabilities for unpaid and incurred but not reported claims totaled $3.4 million, compared to $4.1 million at December 31, 2010. 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. 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, 2011, 2010 and 2009 were $1.3 million, $1.2 million and $0.9 million, respectively. The Company’s obligation under the plan represents an unsecured promise to pay benefits in the future. In the event of bankruptcy or insolvency of the Company, assets of the plan would be available to satisfy the claims of general creditors. To increase the security of the participants’ deferred compensation plan benefits, the Company has established and funded a grantor trust (known as a “rabbi trust”). The rabbi trust is specifically designed so that assets are available to pay plan benefits to participants in the event the Company is unwilling or unable to pay the plan benefits for any reason other than bankruptcy or insolvency. As a result, the Company is prevented from withdrawing or accessing assets for corporate needs. Plan participants choose to receive a return on their account balances equal to the return on various investment options. The Company currently invests plan assets in an equity-based life insurance product of which the rabbi trust is the owner and beneficiary. Effective December 31, 2011, ACI’s Board of Directors terminated the deferred compensation plan. A partial distribution of plan assets was made to participants in May 2011. The Company anticipates making a final distribution of plan assets to participants in the second quarter of 2012. As of December 31, 2011 and 2010, plan assets were $15.3 million and $18.2 million, respectively, and are reflected in prepaid expenses and other current assets in the 2011 presentation and deposits and other assets in the 2010 presentation in the accompanying consolidated balance sheets. The liabilities due the participants were $12.8 million and $15.7 million as of December 31, 2011 and 2010, respectively. In 2011, the liability balance is reflected in accrued liabilities and in 2010, it is reflected in other long-term liabilities in the accompanying consolidated balance sheets. For the years ended December 31, 2011, 2010 and 2009, net deferred compensation expense was $2.1 million, $1.4 million and $0.8 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, $2.1 million and $2.2 million for the years ended December 31, 2011, 2010 and 2009, 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 employee health benefit plan that 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 $28.3 million, $32.0 million and $27.3 million for the years ended December 31, 2011, 2010 and 2009, respectively. At December 31, 2011, estimated liabilities for unpaid and incurred but not reported claims totaled $3.4 million, compared to $4.1 million at December 31, 2010.

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. 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, 2011, 2010 and 2009 were $1.3 million, $1.2 million and $0.9 million, respectively. The Company’s obligation under the plan represents an unsecured promise to pay benefits in the future. In the event of bankruptcy or insolvency of the Company, assets of the plan would be available to satisfy the claims of general creditors. To increase the security of the participants’ deferred compensation plan benefits, the Company has established and funded a grantor trust (known as a “rabbi trust”). The rabbi trust is specifically designed so that assets are available to pay plan benefits to participants in the event the Company is unwilling or unable to pay the plan benefits for any reason other than bankruptcy or insolvency. As a result, the Company is prevented from withdrawing or accessing assets for corporate needs. Plan participants choose to receive a return on their account balances equal to the return on various investment options. The Company currently invests plan assets in an equity-based life insurance product of which the rabbi trust is the owner and beneficiary.

Effective December 31, 2011, ACI’s Board of Directors terminated the deferred compensation plan. A partial distribution of plan assets was made to participants in May 2011. The Company anticipates making a final distribution of plan assets to participants in the second quarter of 2012. As of December 31, 2011 and 2010, plan assets were $15.3 million and $18.2 million, respectively, and are reflected in prepaid expenses and other current assets in the 2011 presentation and deposits and other assets in the 2010 presentation in the accompanying consolidated balance sheets. The liabilities due the participants were $12.8 million and $15.7 million as of December 31, 2011 and 2010, respectively. In 2011, the liability balance is reflected in accrued liabilities and in 2010, it is reflected in other long-term liabilities in the accompanying consolidated balance sheets. For the years ended December 31, 2011, 2010 and 2009, net deferred compensation expense was $2.1 million, $1.4 million and $0.8 million, respectively.