Financial Instruments and Concentrations of Risk (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) employees	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Margin deposits	$ 100	$ 1,900
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 3,800	500
Number of Employees, Geographic Area [Member] \| Geographic Concentration Risk [Member]
Number of employees \| employees	880
CANADA \| Number of Employees, Geographic Area [Member] \| Geographic Concentration Risk [Member]
Number of employees	265
CANADA \| Workforce Subject to Collective Bargaining Arrangements [Member] \| Unionized Employees Concentration Risk [Member]
Number of employees	55
Largest Customer [Member] \| Sales Revenue, Net [Member] \| Customer Concentration Risk [Member]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 645,000
Largest Customer [Member] \| Cost of Goods, Total [Member] \| Supplier Concentration Risk [Member]
Cost of Goods and Services Sold	$ 248,700
Largest Customer [Member] \| Accounts Receivable [Member] \| Customer Concentration Risk [Member]
Concentration of risk, percentage	28.00%
Three Largest Producers [Member] \| Processing volumes [Member] \| Product Concentration Risk [Member] \| U.S. Gas [Member]
Concentration of risk, percentage	89.00%
Two Largest Producers [Member] \| Gathering volumes [Member] \| Product Concentration Risk [Member] \| U.S. Gas [Member]
Concentration of risk, percentage	83.00%
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member]
Derivative, Notional Amount	$ 524,300	491,100
Not Designated as Hedging Instrument [Member] \| Foreign Exchange Forward [Member]
Derivative, Notional Amount	56,100	197,700
Realized/Unrealized (gain) loss included in earnings	10,200	(2,800)
Not Designated as Hedging Instrument [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swap [Member]
Derivative Assets (Liabilities), at Fair Value, Net	(1,482)	(1,228)	$ 0
Realized/Unrealized (gain) loss included in earnings	163	(1,124)
Fair Value, Measurements, Recurring [Member]
Derivative Assets (Liabilities), at Fair Value, Net	(782)	(32)
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Derivative Assets (Liabilities), at Fair Value, Net	(1,482)	(1,228)
Derivative Liability, Fair Value, Gross Liability	1,482	1,228
Derivative Asset	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative Assets (Liabilities), at Fair Value, Net	(2,985)	2,564
Derivative Liability, Fair Value, Gross Liability	2,985	0
Derivative Asset	0	2,564
Fair Value, Measurements, Recurring [Member] \| Not Designated as Hedging Instrument [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swap [Member]
Derivative Liability, Fair Value, Gross Liability	1,482	1,228
Fair Value, Measurements, Recurring [Member] \| Not Designated as Hedging Instrument [Member] \| Fair Value, Inputs, Level 2 [Member] \| Foreign Exchange Forward [Member]
Derivative Liability, Fair Value, Gross Liability	$ 2,985
Derivative Asset		$ 2,564

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Purchases of Product

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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