Debt (Tables)

12 Months Ended

Dec. 31, 2015

Long-term Debt, Current and Noncurrent [Abstract]

Schedule of Maturities of Long-term Debt [Table Text Block]

In thousands
Year
2016	$	25,000
2017	40,000
2018	22,000
2019	30,000
2020	75,000
Thereafter	409,700

Schedule of Debt [Table Text Block]

In thousands	2015		2014
First Mortgage Bonds
4.70 % Series B due 2015	—		40,000
5.15 % Series B due 2016	25,000		25,000
7.00 % Series B due 2017	40,000		40,000
6.60 % Series B due 2018	22,000		22,000
8.31 % Series B due 2019	10,000		10,000
7.63 % Series B due 2019	20,000		20,000
5.37 % Series B due 2020	75,000		75,000
9.05 % Series A due 2021	10,000		10,000
3.176 % Series B due 2021	50,000		50,000
3.542% Series B due 2023	50,000		50,000
5.62 % Series B due 2023	40,000		40,000
7.72 % Series B due 2025	20,000		20,000
6.52 % Series B due 2025	10,000		10,000
7.05 % Series B due 2026	20,000		20,000
7.00 % Series B due 2027	20,000		20,000
6.65 % Series B due 2027	19,700		19,700
6.65 % Series B due 2028	10,000		10,000
7.74 % Series B due 2030	20,000		20,000
7.85 % Series B due 2030	10,000		10,000
5.82 % Series B due 2032	30,000		30,000
5.66 % Series B due 2033	40,000		40,000
5.25 % Series B due 2035	10,000		10,000
4.00 % due 2042	50,000		50,000
	601,700		641,700
Subsidiary Senior Secured Debt
Gill Ranch debt due 2016	—		20,000
	601,700		661,700
Less: Current maturities	25,000		40,000
Total long-term debt	$	576,700	$	621,700

Fair Value Of Long Term Debt Table [Text Block]

	December 31,
In thousands	2015		2014
Carrying amount	$	601,700	$	661,700
Estimated fair value	667,168		756,808