STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Comprehensive income:
Net income	$ 32,211	$ 22,576	$ 54,734	$ 42,823
Pension and retiree medical benefits:
Net Amortization of losses included in net periodic benefit cost, net of tax of $6, $0, $13 and $0, respectively	11	0	23	0
Derivative instruments:
Reclassification of losses to net income, net of tax of $24, $24, $49 and $48, respectively	43	43	85	85
Other comprehensive income	54	43	108	85
Comprehensive income	$ 32,265	$ 22,619	$ 54,842	$ 42,908