Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Net income	$ 37,325	$ 13,829
Net unrealized gain on derivative instruments qualifying as hedges:
Reclassification adjustment for loss on derivative instruments included in net income, net of tax of $56 and $57 for the three months ended in 2017 and 2016, respectively	91	92
Postretirement liability adjustment:
Amortization of postretirement liability (gains) losses included in net periodic benefit cost, net of tax of $217 and $(969) for the three months ended in 2017 and 2016, respectively	357	(1,595)
Reclassification of postretirement liability adjustment from regulatory asset, net of tax of $(725) and $0 for the three months ended in 2017 and 2016, respectively	(917)	0
Postretirement liability adjustment	(560)	(1,595)
Foreign currency translation adjustment:
Foreign currency translation adjustment recognized during the period, net of tax of $5 and $15 for the three months ended in 2017 and 2016, respectively	9	25
Net unrealized gain on available-for-sale investments:
Net unrealized gain (loss) on available-for-sale investments arising during the period, net of tax of $(15) and $5 for the three months ended in 2017 and 2016, respectively	(27)	8
Reclassification adjustment for loss on available-for-sale investments included in net income, net of tax of $19 and $19 for the three months ended in 2017 and 2016, respectively	35	36
Net unrealized gain on available-for-sale investments	8	44
Other comprehensive loss	(452)	(1,434)
Comprehensive income	36,873	12,395
Loss from discontinued operations attributable to noncontrolling interest	0	(11,040)
Comprehensive income attributable to common stockholders	$ 36,873	$ 23,435