Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net Income (Loss)	$ (144,372)	$ 36,358
Other comprehensive income, net:
Net change related to employee benefit plans, net of tax expense/benefit	598	576
Net change in derivative instruments, net of tax expense/benefit	344	1,145
Net change in available-for-sale investments, net of tax expense/benefit	389	540
Net current-period other comprehensive income (loss)	1,331	2,261
Total Comprehensive Income (Loss)	$ (143,041)	$ 38,619