Revisions To Financial Statements (Schedule Of Prior Period Financial Statements - Stockholder's Equity) (Details) - USD ($) $ in Thousands	3 Months Ended					6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	$ 5,386,602	$ 5,036,757	$ 5,042,149	$ 5,346,404	$ 5,409,332	$ 5,036,757	$ 5,409,332	$ 5,409,332	$ 5,409,332
Net income (loss)	280,922	251,608	21,966	(267,295)	(11,793)	532,530	(279,088)	(257,122)	(962,184)	$ 79,870
Ending balance,	5,735,239	5,386,602	5,058,645	5,042,149	5,346,404	5,735,239	5,042,149	5,058,645	5,036,757	5,409,332
Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	4,314,306	4,062,696	4,745,792	5,013,087	5,022,433	4,062,696	5,022,433	5,022,433	5,022,433	4,942,239
Net income (loss)	280,922	251,608	21,966	(267,295)	(11,793)		(279,088)	(257,122)	(962,184)	79,870
Ending balance,	4,595,227	4,314,306	4,767,758	4,745,792	5,013,087	4,595,227	4,745,792	4,767,758	4,062,696	5,022,433
As Previously Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	5,394,126	5,044,665	5,047,046	5,349,415	5,412,723	5,044,665	5,412,723	5,412,723	5,412,723
Net income (loss)	281,904	251,226	24,665	(265,408)	(12,172)	533,130	(277,580)	(252,915)	(957,667)	78,198
Ending balance,	5,743,746	5,394,126	5,066,243	5,047,046	5,349,415	5,743,746	5,047,046	5,066,243	5,044,665	5,412,723
As Previously Reported [Member] | Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	4,321,830	4,070,604	4,750,691	5,016,099	5,025,824	4,070,604	5,025,824	5,025,824	5,025,824	4,947,301
Net income (loss)	281,904	251,226	24,665	(265,408)	(12,172)		(277,580)	(252,915)	(957,667)	78,198
Ending balance,	4,603,734	4,321,830	4,775,356	4,750,691	5,016,099	4,603,734	4,750,691	4,775,356	4,070,604	5,025,824
Impact of Revisions [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	(7,524)	(7,908)	(4,897)	(3,011)	(3,391)	(7,908)	(3,391)	(3,391)	(3,391)
Net income (loss)	(982)	382	(2,699)	(1,887)	379	(600)	(1,508)	(4,207)	(4,517)	1,672
Ending balance,	(8,507)	(7,524)	(7,597)	(4,897)	(3,011)	(8,507)	(4,897)	(7,597)	(7,908)	(3,391)
Impact of Revisions [Member] | Retained Earnings [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Beginning balance,	(7,524)	(7,908)	(4,897)	(3,011)	(3,391)	(7,908)	(3,391)	(3,391)	(3,391)	(5,062)
Net income (loss)	(982)	382	(2,699)	(1,887)	379		(1,508)	(4,207)	(4,517)	1,672
Ending balance,	$ (8,507)	$ (7,524)	$ (7,597)	$ (4,897)	$ (3,011)	$ (8,507)	$ (4,897)	$ (7,597)	$ (7,908)	$ (3,391)