Pension Plans and Other Postretirement Benefits - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Mar. 25, 2017	Sep. 30, 2017
Components of net periodic benefit costs included in operating expenses [Abstract]
Contribution to defined pension benefit plan	$ 1,904	$ 2,792
Estimated obligation due to full withdrawal multi employer pension plans	23,112		$ 23,665
Defined Benefit Pension Plan [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Defined benefit plan expected contribution to be paid for fiscal year	4,764
Contribution to defined pension benefit plan	1,904
Post-Retirement Benefits [Member]
Components of net periodic benefit costs included in operating expenses [Abstract]
Defined benefit plan expected contribution to be paid for fiscal year	1,243
Employer contribution for postretirement health care and life insurance	$ 580