STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Comprehensive income:
Net income	$ 33,099	$ 25,055
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $5 and $9, respectively	19	15
Derivative instruments:
Reclassification of losses to net income, net of tax of $3 and $6, respectively	12	9
Other comprehensive income	31	24
Comprehensive income	$ 33,130	$ 25,079