STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Comprehensive income:
Net income	$ 25,055	$ 22,523
Pension and retiree medical benefits:
Amortization of losses included in net periodic benefit cost, net of tax of $9 and $7, respectively	15	12
Derivative instruments:
Reclassification of losses to net income, net of tax of $6 and $25, respectively	9	42
Other comprehensive income	24	54
Comprehensive income	$ 25,079	$ 22,577