Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 35,575	$ 40,604	$ 57,827	$ 34,775
Other comprehensive income (loss), net:
Net change related to employee benefit plans	44	1,381	389	3,347
Net change in derivative instruments	7,081	(4,465)	(1,726)	2,991
Net change in available-for-sale investments	(90)	0	(55)	0
Total other comprehensive income (loss)	7,035	(3,084)	(1,392)	6,338
Total Comprehensive Income	$ 42,610	$ 37,520	$ 56,435	$ 41,113