Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	$ (6,572)	$ (6,672)
Other comprehensive gain before reclassifications	1,527	(487)
Amounts reclassified from accumulated other comprehensive loss	125	587
Balance at the end of the period	(6,049)	(6,572)
Unrealized Net Loss on Interest Rate Swap
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(1,328)	(1,195)
Other comprehensive gain before reclassifications	327	(338)
Amounts reclassified from accumulated other comprehensive loss	(246)	205
Balance at the end of the period	(1,530)	(1,328)
Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	1,392	937
Other comprehensive gain before reclassifications	683	521
Amounts reclassified from accumulated other comprehensive loss	(158)	(66)
Balance at the end of the period	2,118	1,392
Pension Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(6,636)	(6,414)
Other comprehensive gain before reclassifications	517	(670)
Amounts reclassified from accumulated other comprehensive loss	529	448
Balance at the end of the period	(6,637)	$ (6,636)
ASC 2014-09
Changes to accumulated other comprehensive loss by component
Impact due to adoption	377
ASU 2018-02
Changes to accumulated other comprehensive loss by component
Impact due to adoption	(1,129)
Balance at the end of the period	(1,129)
ASU 2018-02 \| Unrealized Net Loss on Interest Rate Swap
Changes to accumulated other comprehensive loss by component
Impact due to adoption	(283)
ASU 2018-02 \| Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Impact due to adoption	201
ASU 2018-02 \| Pension Liability
Changes to accumulated other comprehensive loss by component
Impact due to adoption	$ (1,047)

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

+ References

No definition available.

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- Definition

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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