Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 3,658,972	$ 4,654,574
Other comprehensive income (loss) before reclassifications	(2,136)	508
Amounts reclassified from AOCI	568	550
Other comprehensive income (loss), net	(1,568)	1,058
Ending Balance	2,596,532	4,583,808
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(40,635)	(39,058)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI	568	550
Other comprehensive income (loss), net	568	550
Ending Balance	(40,067)	(38,508)
Foreign Currency Items
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(17,754)	(18,014)
Other comprehensive income (loss) before reclassifications	(2,136)	508
Amounts reclassified from AOCI	0	0
Other comprehensive income (loss), net	(2,136)	508
Ending Balance	(19,890)	(17,506)
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(58,389)	(57,072)
Other comprehensive income (loss), net	(1,568)	1,058
Ending Balance	$ (59,957)	$ (56,014)