Revisions To Financial Statements (Schedule Of Prior Period Financial Statements - Operations And Comprehensive Income (Loss)) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REVENUES:
Other income (expense)			$ (18,225)	$ (3,300)		$ (13,408)	$ (6,573)	$ 17,033	$ (21,525)	$ 10,460	$ (2,948)	$ (11,034)	$ (24,771)	$ (21,215)
Total revenues			2,008,727	1,965,836		1,936,463	1,883,330	1,750,126	3,974,563	3,633,456	5,569,919	8,231,169	7,361,495	6,622,298
INCOME (LOSS) BEFORE TAXES			372,345	414,544		189,471	51,154	222,612	786,889	273,766	463,237	1,098,987	(242,182)	419,411
Income tax expense (benefit)			39,477	59,993		(8,910)	(9,633)	7,426	99,470	(2,207)	(11,117)	89,526	(331,223)	(63,340)
NET INCOME (LOSS)	$ 217,644	$ 104,398	332,868	354,551	$ (385,313)	198,381	60,787	215,186	687,419	275,973	474,354	1,009,461	89,041	482,751
COMPREHENSIVE INCOME (LOSS)			$ 504,077	$ 600,997		$ 173,402	$ (42,577)	$ 35,304	$ 1,105,074	$ (7,273)	$ 166,129	$ 1,500,170	$ (211,424)	$ 539,874
EARNINGS PER COMMON SHARE:
Basic	$ 5.34	$ 2.56	$ 8.17	$ 8.70	$ (9.58)	$ 4.87	$ 1.49	$ 5.26	$ 16.88	$ 6.75	$ 11.61	$ 24.77	$ 2.18	$ 11.77
Diluted	$ 5.32	$ 2.56	$ 8.15	$ 8.67	$ (9.58)	$ 4.84	$ 1.48	$ 5.23	$ 16.82	$ 6.71	$ 11.55	$ 24.70	$ 2.17	$ 11.70
As Previously Reported [Member]
REVENUES:
Other income (expense)			$ (7,977)	$ (9,053)		$ (5,458)	$ 3,036	$ 12,064	$ (17,030)	$ 15,100	$ 9,642		$ (9,060)	$ (35,442)
Total revenues			2,018,975	1,960,083		1,944,413	1,892,939	1,745,157	3,979,058	3,638,096	5,582,509		7,377,206	6,608,071
INCOME (LOSS) BEFORE TAXES			382,593	408,791		197,421	60,763	217,643	791,384	278,406	475,827		(226,471)	405,184
Income tax expense (benefit)			39,738	59,891		(8,192)	(9,132)	7,325	99,629	(1,807)	(9,999)		(330,023)	(63,784)
NET INCOME (LOSS)			342,855	348,900		205,613	69,895	210,318	691,755	280,213	485,826		103,552	468,968
COMPREHENSIVE INCOME (LOSS)			$ 514,064	$ 595,346		$ 180,634	$ (33,469)	$ 30,436	$ 1,109,410	$ (3,033)	$ 177,601		$ (196,913)	$ 526,091
EARNINGS PER COMMON SHARE:
Basic			$ 8.42	$ 8.57		$ 5.04	$ 1.71	$ 5.14	$ 16.98	$ 6.85	$ 11.89		$ 2.54	$ 11.43
Diluted			$ 8.39	$ 8.54		$ 5.02	$ 1.70	$ 5.11	$ 16.93	$ 6.81	$ 11.83		$ 2.53	$ 11.36
Impact of Revisions [Member]
REVENUES:
Other income (expense)			$ (10,248)	$ 5,753		$ (7,950)	$ (9,609)	$ 4,969	$ (4,495)	$ (4,640)	$ (12,590)		$ (15,711)	$ 14,227
Total revenues			(10,248)	5,753		(7,950)	(9,609)	4,969	(4,495)	(4,640)	(12,590)		(15,711)	14,227
INCOME (LOSS) BEFORE TAXES			(10,248)	5,753		(7,950)	(9,609)	4,969	(4,495)	(4,640)	(12,590)		(15,711)	14,227
Income tax expense (benefit)			(261)	102		(718)	(501)	101	(159)	(400)	(1,118)		(1,200)	444
NET INCOME (LOSS)			(9,987)	5,651		(7,232)	(9,108)	4,868	(4,336)	(4,240)	(11,472)		(14,511)	13,783
COMPREHENSIVE INCOME (LOSS)			$ (9,987)	$ 5,651		$ (7,232)	$ (9,108)	$ 4,868	$ (4,336)	$ (4,240)	$ (11,472)		$ (14,511)	$ 13,783
EARNINGS PER COMMON SHARE:
Basic			$ (0.25)	$ 0.13		$ (0.17)	$ (0.22)	$ 0.12	$ (0.10)	$ (0.10)	$ (0.28)		$ (0.36)	$ 0.34
Diluted			$ (0.24)	$ 0.13		$ (0.18)	$ (0.22)	$ 0.12	$ (0.11)	$ (0.10)	$ (0.28)		$ (0.36)	$ 0.34