Derivative Instruments - Schedule of Unrealized and Realized Gain/Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
General Discussion of Derivative Instruments and Hedging Activities [Abstract]
Derivative, Loss on Derivative	$ 7,400	$ 7,800
Northwest Holdings and Northwest Natural [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	0	0
Northwest Holdings and Northwest Natural [Member] | Foreign Exchange Contract [Member] | Cost of Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(284)	107
Northwest Holdings and Northwest Natural [Member] | Foreign Exchange Contract [Member] | Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	0	0
Northwest Holdings and Northwest Natural [Member] | Natural Gas Commodity [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	210	(356)
Northwest Holdings and Northwest Natural [Member] | Natural Gas Commodity [Member] | Cost of Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	(1,239)	26,000
Northwest Holdings and Northwest Natural [Member] | Natural Gas Commodity [Member] | Sales [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	1,660	(1,021)
Northwest Holdings and Northwest Natural [Member] | Deferred Derivative Gain (Loss) [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	284	(107)
Northwest Holdings and Northwest Natural [Member] | Deferred Derivative Gain (Loss) [Member] | Natural Gas Commodity [Member]
Derivative [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax	$ (211)	$ 26,665