CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Comprehensive income:
Net income	$ 115,874	$ 110,966
Net pension and retiree medical benefits losses arising during the period, net of tax of $135 and $0, respectively	(219)	0
Derivative instruments:
Net fair value decrease, net of tax of $(1) and $(3), respectively	(2)	(5)
Reclassification of losses (gains) to net income, net of tax of $163 and $(64), respectively	264	(105)
Other comprehensive income (loss)	43	(110)
Comprehensive income	$ 115,917	$ 110,856