Nonqualified Deferred Compensation Plan	12 Months Ended
Sep. 26, 2015
Compensation Related Costs [Abstract]
Nonqualified Deferred Compensation Plan	Deferred Compensation Plans Nonqualified Deferred Compensation Plan Effective March 15, 2006, the Company adopted its DCP to provide non-qualified retirement benefits to a select group of executive officers, senior management and highly compensated employees of the Company. Eligible employees may elect to contribute up to 75% of their annual base salary and 100% of their annual bonus to the DCP and such employee contributions are 100% vested. In addition, the Company may elect to make annual discretionary contributions on behalf of participants in the DCP. Each Company contribution is subject to a three-year vesting schedule, such that each contribution vests one third annually. Employee contributions are recorded within accrued expenses. Upon enrollment into the DCP, employees make investment elections for both their voluntary contributions and discretionary contributions, if any, made by the Company. Earnings and losses on contributions based on these investment elections are recorded as a component of compensation expense in the period earned. Annually, the Compensation Committee of the Board of Directors has approved a discretionary cash contribution to the DCP for each year. Discretionary contributions by the Company to the DCP are held in a Rabbi Trust. The Company is recording compensation expense for the DCP discretionary contributions ratably over the three-year vesting period of each annual contribution, which totaled $1.8 million, $3.7 million and $2.7 million in fiscal 2015, 2014 and 2013, respectively. The full amount of the discretionary contribution, net of forfeitures, along with employee deferrals is recorded within accrued expenses and totaled $29.4 million and $35.8 million at September 26, 2015 and September 27, 2014, respectively. The Company has purchased Company-owned group life insurance contracts, in which both voluntary and discretionary Company DCP contributions are invested, to partially fund payment of the Company’s obligation to the DCP participants. The total amount invested at September 26, 2015 and September 27, 2014 was $27.5 million and $22.4 million, respectively. The values of these life insurance contracts are recorded in other long-term assets. Changes in the cash surrender value of life insurance contracts, which were not significant in fiscal 2015, 2014 and 2013, are recorded within other income (expense), net. In addition, the Company had an additional $5.6 million and $15.4 million of investments in mutual funds to fund the DCP at September 26, 2015 and September 27, 2014, respectively. The mutual funds are classified as trading and the gains and losses in these investments are recorded in other income (expense), net. Deferred Equity Plan Effective September 17, 2015, the Company adopted the Hologic, Inc. Deferred Equity Plan (the “DEP”). The DEP is designed to allow executives and non-employee Directors to accumulate Company stock in a tax-efficient manner to meet their long-term equity accumulation goals and shareholder ownership guidelines. Under the DEP, eligible participants may elect to defer the settlement of RSUs and PSUs granted under the 2008 Equity Plan until separation from service or separation from service plus a fixed number of years. Participants may defer settlement by vesting tranche. Although the equity will vest on schedule, if deferral of settlement is elected, no shares will be issued until the settlement date. The settlement date will be the earlier of death, disability, change in control of the Company or separation from service plus the number of years of deferral elected by the participant.

Deferred Compensation Plans

Nonqualified Deferred Compensation Plan

Effective March 15, 2006, the Company adopted its DCP to provide non-qualified retirement benefits to a select group of executive officers, senior management and highly compensated employees of the Company. Eligible employees may elect to contribute up to 75% of their annual base salary and 100% of their annual bonus to the DCP and such employee contributions are 100% vested. In addition, the Company may elect to make annual discretionary contributions on behalf of participants in the DCP. Each Company contribution is subject to a three-year vesting schedule, such that each contribution vests one third annually. Employee contributions are recorded within accrued expenses.

Upon enrollment into the DCP, employees make investment elections for both their voluntary contributions and discretionary contributions, if any, made by the Company. Earnings and losses on contributions based on these investment elections are recorded as a component of compensation expense in the period earned.

Annually, the Compensation Committee of the Board of Directors has approved a discretionary cash contribution to the DCP for each year. Discretionary contributions by the Company to the DCP are held in a Rabbi Trust. The Company is recording compensation expense for the DCP discretionary contributions ratably over the three-year vesting period of each annual contribution, which totaled $1.8 million, $3.7 million and $2.7 million in fiscal 2015, 2014 and 2013, respectively. The full amount of the discretionary contribution, net of forfeitures, along with employee deferrals is recorded within accrued expenses and totaled $29.4 million and $35.8 million at September 26, 2015 and September 27, 2014, respectively.

The Company has purchased Company-owned group life insurance contracts, in which both voluntary and discretionary Company DCP contributions are invested, to partially fund payment of the Company’s obligation to the DCP participants. The total amount invested at September 26, 2015 and September 27, 2014 was $27.5 million and $22.4 million, respectively. The values of these life insurance contracts are recorded in other long-term assets. Changes in the cash surrender value of life insurance contracts, which were not significant in fiscal 2015, 2014 and 2013, are recorded within other income (expense), net. In addition, the Company had an additional $5.6 million and $15.4 million of investments in mutual funds to fund the DCP at September 26, 2015 and September 27, 2014, respectively. The mutual funds are classified as trading and the gains and losses in these investments are recorded in other income (expense), net.

Deferred Equity Plan

Effective September 17, 2015, the Company adopted the Hologic, Inc. Deferred Equity Plan (the “DEP”). The DEP is designed to allow executives and non-employee Directors to accumulate Company stock in a tax-efficient manner to meet their long-term equity accumulation goals and shareholder ownership guidelines. Under the DEP, eligible participants may elect to defer the settlement of RSUs and PSUs granted under the 2008 Equity Plan until separation from service or separation from service plus a fixed number of years. Participants may defer settlement by vesting tranche. Although the equity will vest on schedule, if deferral of settlement is elected, no shares will be issued until the settlement date. The settlement date will be the earlier of death, disability, change in control of the Company or separation from service plus the number of years of deferral elected by the participant.