Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 214,409	$ 210,400	$ 425,319	$ 433,136
Other comprehensive income:
Net gain (loss) on cash flow hedges	1,697	(2,802)	7,111	(1,507)
Reclassification of net loss on cash flow hedges to income	739	739	1,479	1,479
Net actuarial loss	653	0	(5,291)	0
Amortization of prior service credit	(46)	(46)	(91)	(91)
Amortization of actuarial loss	1,703	1,983	6,817	3,211
Settlement cost	0	361	0	1,726
Total other comprehensive income	4,746	235	10,025	4,818
Comprehensive income	$ 219,155	$ 210,635	$ 435,344	$ 437,954