STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Comprehensive income:
Net income	$ 22,523	$ 20,247
Net pension and retiree medical benefits losses arising during the period, net of tax of $7 and $0, respectively	12	0
Derivative instruments:
Reclassification of losses to net income, net of tax of $25 and $24, respectively	42	42
Other comprehensive income	54	42
Comprehensive income	$ 22,577	$ 20,289