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)		1,359,048	(85)	1,358,963
Stock-based compensation	19,539			19,539
Contributions from (distributions to) member, net	11,247			11,247
Other	(3,486)	(4)		(3,490)
Balance at end of period at Sep. 30, 2019	3,506,044	2,358,750	9,482	5,874,276
Balance at beginning of period at Jun. 30, 2019	3,495,633	2,258,081	9,510	5,763,224
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		100,668	(28)	100,640
Stock-based compensation	5,775			5,775
Contributions from (distributions to) member, net	4,706			4,706
Other	(70)	1		(69)
Balance at end of period at Sep. 30, 2019	3,506,044	2,358,750	9,482	5,874,276
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)		1,018,717	(77)	1,018,640
Stock-based compensation	11,477			11,477
Contributions from (distributions to) member, net	27,053			27,053
Other	(1,862)	(2,982)		(4,844)
Balance at end of period at Sep. 30, 2020	3,348,068	4,201,604	8,723	7,558,395
Balance at beginning of period at Jun. 30, 2020	3,325,119	3,194,616	8,749	6,528,484
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)		1,006,989	(26)	1,006,963
Stock-based compensation	4,822			4,822
Contributions from (distributions to) member, net	18,682			18,682
Other	(555)	(1)		(556)
Balance at end of period at Sep. 30, 2020	$ 3,348,068	$ 4,201,604	$ 8,723	$ 7,558,395