Transactions with Major Customers and Affiliates (Tables)

12 Months Ended

Dec. 31, 2017

Transactions with Major Customers and Affiliates [Abstract]

Schedule of revenue by major customers

During the periods presented, more than 10 percent of our operating revenues were generated from each of the following customers:

	Years Ended December 31,
	2017		2016		2015
	(Thousands of Dollars)
Puget Sound Energy, Inc.	$	120,226	$	120,351	$	118,384
Northwest Natural Gas Company	51,743		49,895		50,857
Cascade Natural Gas Corporation	48,071		47,951		48,363