STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Comprehensive income:
Net income	$ 68,346	$ 61,815	$ 123,080	$ 104,638
Pension and retiree medical benefits:
Net Amortization of losses included in net periodic benefit cost, net of tax of $6, $0, $19 and $0, respectively	12	0	35	0
Derivative instruments:
Reclassification of losses to net income, net of tax of $25, $24, $74 and $72, respectively	44	44	129	129
Other comprehensive income	56	44	164	129
Comprehensive income	$ 68,402	$ 61,859	$ 123,244	$ 104,767