Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

In thousands	2020		2019		2018
Operations and maintenance expense, for stock-based compensation	$	3,525	$	2,172	$	2,489
Income tax benefit	(933)		(575)		(659)
Net stock-based compensation effect on net income (loss)	2,592		1,597		1,830
Amounts capitalized for stock-based compensation	$	841	$	430	$	531

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Option Shares	Weighted - Average Price Per Share		Intrinsic Value (In millions)
Balance outstanding and exercisable, December 31, 2017	91,688	$	44.43	$	1.4
Exercised	(35,450)	43.61		0.8
Forfeited	(300)	43.29		n/a
Balance outstanding and exercisable, December 31, 2018	55,938	44.96		0.9
Exercised	(45,000)	44.79		1.0
Forfeited	—	—		n/a
Balance outstanding and exercisable, December 31, 2019	10,938	45.67		0.3
Exercised	(1,500)	45.24		—
Expired	—	—		n/a
Balance outstanding and exercisable, December 31, 2020	9,438	$	45.74	$	—

Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block]

	Number of RSUs	Weighted - Average Price Per RSU
Nonvested, December 31, 2017	84,522	$	53.90
Granted	32,450	57.59
Vested	(32,689)	50.75
Forfeited	(1,603)	59.95
Nonvested, December 31, 2018	82,680	56.47
Granted	36,018	65.29
Vested	(35,778)	54.22
Forfeited	(3,187)	63.89
Nonvested, December 31, 2019	79,733	61.17
Granted	33,594	55.58
Vested	(29,273)	59.29
Forfeited	(1,590)	69.71
Nonvested, December 31, 2020	82,464	$	59.40

Share-based Payment Arrangement, Performance Shares, Outstanding Activity [Table Text Block]

The aggregate number of performance shares granted and outstanding at the target and maximum levels were as follows:

Dollars in thousands	Performance Share Awards Outstanding		2020
Performance Period	Target	Maximum	Expense
2018-20	31,825	63,650	$	2,137
2019-21	—	—	—
2020-22	—	—	—
Total	31,825	63,650	$	2,137

Long Term Incentive Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share-based Compensation Arrangements by Share-based Payment Award, Performance-Based Units, Vested and Expected to Vest [Table Text Block]

The following table summarizes performance share expense information:

Dollars in thousands	Shares(1)	Expense During Award Year(2)		Total Expense for Award
Estimated award:
2018-2020 grant(3)	31,600	$	2,137	$	2,137
Actual award:
2017-2019 grant	41,537	$	572	$	1,971
2016-2018 grant	28,218	$	598	$	1,413

(1)     In addition to common stock shares, a participant also receives a dividend equivalent cash payment equal to the number of shares of common stock received on the award payout multiplied by the aggregate cash dividends paid per share during the performance period.

(2)     Amount represents the expense recognized in the third year of the vesting period noted above. For the 2018-2020 grant, mutual understanding of the award's key terms was established in the third year of the vesting period, triggering full expense recognition in 2020.

(3)    This represents the estimated number of shares to be awarded as of December 31, 2020 as certain performance share measures have been achieved. Amounts are subject to change with final payout amounts authorized by the Board of Directors in February 2021.