Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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Derivative Financial Instruments and Hedging - Additional Information (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
Derivative [Line Items]
Unrealized gain (loss) on derivative contracts	$ 4,700
Accumulated other comprehensive income loss					$ (4,015)	$ 2,957
Interest rate swap agreements
Derivative [Line Items]
Interest rate swap agreement, current liability	87		$ 87		$ 1,163	$ 3,888
Non-Designated \| Foreign Exchange Forward
Derivative [Line Items]
Derivative term (in years)			1 year		1 year
Unrealized gain (loss) on derivative contracts					$ 2,100
Cash Flow Hedging \| Designated \| Foreign Currency Contracts
Derivative [Line Items]
Derivative term (in years)			2 years
Derivative instruments amounts reclassified into income	0	$ 0	$ 0	$ 0
Cash Flow Hedging \| Designated \| Foreign Exchange Forward
Derivative [Line Items]
Derivative term (in years)					2 years
Derivative instruments amounts reclassified into income					$ 400
Fair Value Hedging \| Designated \| Interest rate swap agreements
Derivative [Line Items]
Interest rate swap agreement, current liability	100		100		1,200
Accumulated other comprehensive income loss	$ 100		$ 100		$ 700