Condensed Consolidated Statements of Equity (unaudited) - USD ($) $ in Thousands	Member's Investment	Retained earnings [Member]	Non-controlling interest in equity of subsidiaries [Member]	Total
Balance at beginning of period at Dec. 31, 2018	$ 3,478,744	$ 999,706	$ 9,567	$ 4,488,017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		1,258,380	(57)	1,258,323
Stock-based compensation	13,764			13,764
Contributions from (distributions to) member, net	6,541			6,541
Other	(3,416)	(5)		(3,421)
Balance at end of period at Jun. 30, 2019	3,495,633	2,258,081	9,510	5,763,224
Balance at beginning of period at Mar. 31, 2019	3,488,093	1,749,932	9,510	5,247,535
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		508,150		508,150
Stock-based compensation	7,029			7,029
Contributions from (distributions to) member, net	2,013			2,013
Other	(1,502)	(1)		(1,503)
Balance at end of period at Jun. 30, 2019	3,495,633	2,258,081	9,510	5,763,224
Balance at beginning of period at Dec. 31, 2019	3,311,400	3,185,869	8,800	6,506,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		11,728	(51)	11,677
Stock-based compensation	6,655			6,655
Contributions from (distributions to) member, net	8,371			8,371
Other	(1,307)	(2,981)		(4,288)
Balance at end of period at Jun. 30, 2020	3,325,119	3,194,616	8,749	6,528,484
Balance at beginning of period at Mar. 31, 2020	3,316,580	2,542,848	8,775	5,868,203
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		651,768	(26)	651,742
Stock-based compensation	4,106			4,106
Contributions from (distributions to) member, net	4,659			4,659
Other	(226)			(226)
Balance at end of period at Jun. 30, 2020	$ 3,325,119	$ 3,194,616	$ 8,749	$ 6,528,484