Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Summary of estimated coal take-or-pay commitments

The following table summarizes our estimated coal take-or-pay commitments (dollars in thousands):

	Years Ended December 31,
	2018		2019		2020		2021		2022		Thereafter
Coal take-or-pay commitments (a)	$	159,997	$	185,365	$	186,632	$	190,607	$	194,678	$	1,750,739

(a) Total take-or-pay commitments are approximately $2.7 billion.  The total net present value of these commitments is approximately $1.9 billion.

Summary of actual take-or-pay commitments

	Year Ended December 31,
	2017		2016		2015
Total purchases	$	165,220	$	160,066	$	211,327