CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Comprehensive income:
Net income	$ 1,123,379	$ 984,485	$ 1,021,306
Pension and retiree medical benefits:
Net pension and retiree medical losses arising during the period, net of tax of $(4,944), $(5,026), and $(4,687), respectively	(7,783)	(7,906)	(7,517)
Amortization of losses included in net periodic benefit cost, net of tax of $2,185, $2,249, and $2,159, respectively	3,471	3,526	3,495
Total pension and retiree medical benefits, net of tax	(4,312)	(4,380)	(4,022)
Derivative instruments:
Net fair value increase (decrease), net of tax of $2, $(46), and $(103), respectively	3	(70)	(163)
Reclassification of losses to net income, net of tax of $2,342, $1,810, and $1,493, respectively	3,708	2,836	2,288
Total derivative instruments, net of tax	3,711	2,766	2,125
Marketable securities:
Net fair value increase, net of tax of $0, $0, and $21, respectively	0	0	33
Other comprehensive loss	(601)	(1,614)	(1,864)
Comprehensive income	$ 1,122,778	$ 982,871	$ 1,019,442