Stock-Based Compensation	3 Months Ended
Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Our stock-based compensation plans are designed to promote stock ownership in NW Natural by employees and officers. These compensation plans include a Long Term Incentive Plan (LTIP), an Employee Stock Purchase Plan (ESPP), and a Restated Stock Option Plan. For additional information on our stock-based compensation plans, see Note 6 in the 2017 Form 10-K and the updates provided below. Long Term Incentive Plan Performance Shares LTIP performance shares incorporate a combination of market, performance, and service-based factors. During the three months ended March 31, 2018, no performance-based shares were granted under the LTIP for accounting purposes. In February 2018, the 2018 LTIP was awarded to participants; however, the agreement allows for one of the performance factors to remain variable until the first quarter of the third year of the award period. As the performance factor will not be approved until the first quarter of 2020, there is not a mutual understanding of the award’s key terms and conditions between the Company and the participants as of March 31, 2018 and expense was not recognized for the 2018 award. We will calculate the grant date fair value and recognize expense once the final performance factor has been approved. For the 2018 LTIP, award share payouts range from a threshold of 0% to a maximum of 200% based on achievement of pre-established goals. The performance criteria for the 2018 performance shares consists of a three-year Return on Invested Capital (ROIC) threshold that must be satisfied and a cumulative EPS factor, which can be modified by a total shareholder return factor (TSR modifier) relative to the performance of the Russell 2500 Utilities Index over the three-year performance period. If the target was achieved for the 2018 award, we would grant 34,702 shares in the first quarter of 2020. As of March 31, 2018, there was $2.3 million of unrecognized compensation cost associated with the 2016 and 2017 LTIP grants, which is expected to be recognized through 2019. Restricted Stock Units During the three months ended March 31, 2018, 23,036 RSUs were granted under the LTIP with a grant date fair value of $54.65 per share. Generally, the RSUs awarded are forfeitable and include a performance-based threshold as well as a vesting period of four years from the grant date. An RSU obligates us, upon vesting, to issue the RSU holder one share of common stock plus a cash payment equal to the total amount of dividends paid per share between the grant date and vesting date of that portion of the RSU. The fair value of an RSU is equal to the closing market price of our common stock on the grant date. As of March 31, 2018, there was $3.5 million of unrecognized compensation cost from grants of RSUs, which is expected to be recognized over a period extending through 2022.

Our stock-based compensation plans are designed to promote stock ownership in NW Natural by employees and officers. These compensation plans include a Long Term Incentive Plan (LTIP), an Employee Stock Purchase Plan (ESPP), and a Restated Stock Option Plan. For additional information on our stock-based compensation plans, see Note 6 in the 2017 Form 10-K and the updates provided below.

Long Term Incentive Plan

Performance Shares

LTIP performance shares incorporate a combination of market, performance, and service-based factors. During the three months ended March 31, 2018, no performance-based shares were granted under the LTIP for accounting purposes. In February 2018, the 2018 LTIP was awarded to participants; however, the agreement allows for one of the performance factors to remain variable until the first quarter of the third year of the award period. As the performance factor will not be approved until the first quarter of 2020, there is not a mutual understanding of the award’s key terms and conditions between the Company and the participants as of March 31, 2018 and expense was not recognized for the 2018 award. We will calculate the grant date fair value and recognize expense once the final performance factor has been approved.

For the 2018 LTIP, award share payouts range from a threshold of 0% to a maximum of 200% based on achievement of pre-established goals. The performance criteria for the 2018 performance shares consists of a three-year Return on Invested Capital (ROIC) threshold that must be satisfied and a cumulative EPS factor, which can be modified by a total shareholder return factor (TSR modifier) relative to the performance of the Russell 2500 Utilities Index over the three-year performance period. If the target was achieved for the 2018 award, we would grant 34,702 shares in the first quarter of 2020.

As of March 31, 2018, there was $2.3 million of unrecognized compensation cost associated with the 2016 and 2017 LTIP grants, which is expected to be recognized through 2019.

Restricted Stock Units

During the three months ended March 31, 2018, 23,036 RSUs were granted under the LTIP with a grant date fair value of $54.65 per share. Generally, the RSUs awarded are forfeitable and include a performance-based threshold as well as a vesting period of four years from the grant date. An RSU obligates us, upon vesting, to issue the RSU holder one share of common stock plus a cash payment equal to the total amount of dividends paid per share between the grant date and vesting date of that portion of the RSU. The fair value of an RSU is equal to the closing market price of our common stock on the grant date. As of March 31, 2018, there was $3.5 million of unrecognized compensation cost from grants of RSUs, which is expected to be recognized over a period extending through 2022.