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EMPLOYEE BENEFIT PLANS (Settlement distributions and expense) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Distributions and pension settlement expense
Pension settlement expense, pre-tax		$ 4,156	$ 3,229	$ 3,202
Nonunion Defined Benefit Pension Plan
Distributions and pension settlement expense
Pension settlement distributions		26,261	16,515	20,622
Pension settlement expense, pre-tax		$ 4,156	$ 3,023	$ 3,202
Pension settlement expense per diluted share, net of taxes		$ 0.10	$ 0.07	$ 0.07
Lump-sum distributions		$ 18,700
Premium paid to purchase nonparticipating annuity contract	$ 7,600	7,600
Supplemental Benefit Plan
Distributions and pension settlement expense
Pension settlement distributions		$ 989	$ 246	$ 1,941
Pension settlement expense, pre-tax			$ 206
Pension settlement expense per diluted share, net of taxes			$ 0.01
Period of delay for pension settlement distribution to key employees			6 months		6 months

X

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

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- Definition

The amount of lump sum benefit distributions paid.

+ References

No definition available.

+ Details

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X

- Definition

Represents the period of delay provision for key employees as required by Section 409A of the Internal Revenue Code related to lump-sum termination payment.

+ References

No definition available.

+ Details

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- Definition

The amount of net gain (loss), per diluted share, net of taxes, recognized in net periodic benefit cost as a result of an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement.

+ References

No definition available.

+ Details

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- Definition

Amount of premium paid for nonparticipating annuity contract to settle vested benefit obligations of participants and beneficiaries receiving monthly benefits.

+ References

No definition available.

+ Details

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- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

+ 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 (h)(7)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

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
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(ii)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(5)(iv)(01)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(8)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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