Pension and retirement plans (Periodic Pension Cost) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 2017	Oct. 01, 2016	Jun. 30, 2018
Components of net periodic pension costs
Service cost	$ 3,868	$ 10,848
Interest cost	5,783	3,774
Expected return on plan assets	(13,757)	(10,588)
Amortization of prior service credits	(393)	(393)
Recognized net actuarial loss	3,746	3,851
Net periodic pension (benefit) cost	(753)	$ 7,492
Plan
Components of net periodic pension costs
Contributions	8,000
Defined benefit plans, estimated future employer contributions each remaining quarter of current fiscal year	8,000
Acquired PF Plan
Components of net periodic pension costs
Contributions	$ 0
Maximum \| Forecast
Components of net periodic pension costs
Settlement			$ 15,000

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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- Definition

Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
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Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

+ References

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- Definition

Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

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Amount of cost recognized for passage of time related to defined benefit plan.

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of payment, which decreases plan assets of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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