Employee Benefit Plans - Components of Net Periodic Benefit Cost (Q3) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Pension Plans \| United States
Net periodic benefit cost
Service cost	$ 87	$ 86	$ 261	$ 258	$ 344	$ 337	$ 381
Interest cost	333	356	999	1,068	1,422	1,475	1,914
Expected return on plan assets	(445)	(433)	(1,335)	(1,299)	(1,731)	(2,076)	(2,168)
Net amortization/deferrals	243	248	729	744	989	914	1,062
Net periodic benefit cost (credit)	218	257	$ 654	$ 771	$ 1,027	$ 653	$ 1,192
Assumptions
Discount Rate			3.56%	3.95%	3.56%	3.95%	4.21%
Expected long-term rate of return			5.15%	4.95%	4.95%	5.70%	5.70%
Rate of compensation increase			3.00%	3.00%	3.00%	3.00%	3.00%
Defined Benefit Pension Plans \| Foreign Plan
Net periodic benefit cost
Service cost	691	614	$ 2,073	$ 1,842	$ 2,740	$ 1,379	$ 2,015
Interest cost	1,834	1,677	5,502	5,031	7,310	5,774	7,091
Expected return on plan assets	(3,466)	(2,910)	(10,398)	(8,730)	(12,412)	(9,971)	(9,591)
Net amortization/deferrals	554	685	1,662	2,055	2,846	1,818	2,379
Net periodic benefit cost (credit)	(387)	66	$ (1,161)	$ 198	$ 1,279	$ (721)	$ 2,106
Assumptions
Discount Rate			2.40%	2.51%	2.40%	2.51%	3.56%
Expected long-term rate of return			5.10%	4.93%	5.02%	6.07%	5.81%
Rate of compensation increase			2.60%	2.54%	2.54%	2.54%	3.10%
Other Postretirement Benefit Plan \| United States
Net periodic benefit cost
Service cost	1	1	$ 3	$ 3	$ 5	$ 4	$ 9
Interest cost	81	88	243	264	350	389	1,233
Net amortization/deferrals	(76)	(73)	(228)	(219)	1,225	1,287	1,356
Net periodic benefit cost (credit)	6	16	$ 18	$ 48	$ 61	$ (29)	$ 303
Assumptions
Discount Rate			3.43%	3.76%	3.43%	3.76%	3.95%
Other Postretirement Benefit Plan \| Foreign Plan
Net periodic benefit cost
Service cost	8	7	$ 24	$ 21	$ 28	$ 29	$ 38
Interest cost	26	24	78	72	98	99	128
Net amortization/deferrals	(4)	(7)	(12)	(21)	(23)	(29)	(30)
Net periodic benefit cost (credit)	$ 30	$ 24	$ 90	$ 72	$ 96	$ 92	$ 129
Assumptions
Discount Rate			3.21%	3.46%	3.21%	3.46%	3.80%

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

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Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

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Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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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.

+ 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)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
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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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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)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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