Shareholders' Equity (Schedule Of Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 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		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Earnings Per Share [Line Items]
Document Period End Date																									Dec. 31, 2019
Net Income (Loss) to Shareholders	$ 511,104	[1]	$ 205,637	[1]	$ 497,298	[1]	$ 576,427	[1]	$ (751,543)	[1]	$ 409,438	[1]	$ 278,231	[1]	$ (64,306)	[1]	$ 434,881	[1]	$ (259,141)	[1]	$ 149,660	[1]	$ 69,869	[1]	$ 1,790,466	[2]	$ (128,180)	[2]	$ 395,269	[2]
Adjustment of redeemable noncontrolling interests																									1,105		(4,828)		(33,738)
Adjusted net income to shareholders																									$ 1,791,571		$ (133,008)		$ 361,531
Basic common shares outstanding																									13,861		13,923		13,964
Diluted shares outstanding																									13,881		13,923		14,006
Basic net income (loss) per share (dollars per share)	$ 36.34		$ 13.97		$ 36.10		$ 42.81		$ (53.88)		$ 28.56		$ 20.01		$ (4.25)		$ 30.48		$ (18.82)		$ 10.34		$ 3.91		$ 129.25		$ (9.55)		$ 25.89
Diluted net income (loss) per share (dollars per share)	$ 36.26		$ 13.95		$ 36.07		$ 42.76		$ (53.88)		$ 28.50		$ 19.97		$ (4.25)		$ 30.39		$ (18.82)		$ 10.31		$ 3.90		$ 129.07	[3]	$ (9.55)	[3]	$ 25.81	[3]
Stock Options [Member]
Earnings Per Share [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements																									0		0		1
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements																									20		0		41
Dilutive potential common shares																									25

[1] Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, the change in fair value of equity securities is no longer recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation.

[2] Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, the change in fair value of equity securities is no longer recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation.

[3] The impact of restricted stock units and restricted stock of 25 thousand shares was excluded from the computation of diluted earnings per share for the year ended December 31, 2018 because the effect would have been anti-dilutive.