6. DEBT

Short-Term Debt

At June 30, 2016, our short-term debt consisted of commercial paper notes payable with a maximum maturity of 67 days and an average maturity of 35 days and an outstanding balance of $152.8 million. The carrying cost of our commercial paper approximates fair value using Level 2 inputs, due to the short-term nature of the notes. See Note 2 in the 2015 Form 10-K for a description of the fair value hierarchy.

Long-Term Debt

At June 30, 2016, we had long-term debt of $595.0 million, which included $6.7 million of unamortized debt issuance costs. Utility long-term debt consists of first mortgage bonds (FMBs) with maturity dates ranging from 2016 through 2042, interest rates ranging from 3.176% to 9.05%, and a weighted-average coupon rate of 5.70%.

Fair Value of Long-Term Debt

Our outstanding debt does not trade in active markets. We estimate the fair value of our debt using inputs from utility companies with similar credit ratings, whose debt trades actively in public markets and has terms and remaining maturities comparable to our own debt. These valuations are based on Level 2 inputs as defined in the fair value hierarchy. See Note 2 in the 2015 Form 10-K for a description of the fair value hierarchy.

The following table provides an estimate of the fair value of our long-term debt, including current maturities of long-term debt, using market prices in effect on the valuation date:



	June 30,						December 31,
In thousands	2016			2015			2015
Gross long-term debt	$	601,700		$	621,700		$	601,700
Unamortized debt issuance costs	(6,668		)	(7,963		)	(7,282		)
Carrying amount	$	595,032		$	613,737		$	594,418
Estimated fair value⁽¹⁾	708,322			695,902			667,168


⁽¹⁾	Estimated fair value does not include unamortized debt issuance costs.