Revision to Prior Year Information (Consolidated Statements of Equity) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Comprehensive income (loss):
Net income (loss)	$ 87,206	$ (136,506)	$ 480,682	$ 159,810
As Previously Reported
Comprehensive income (loss):
Net income (loss)		(134,103)		164,556
Revision
Comprehensive income (loss):
Net income (loss)		(2,403)		(4,746)
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			3,635,147	3,557,144
Comprehensive income (loss):
Net income (loss)			480,682	159,810
Balance, ending	1,522,310	3,486,954	1,522,310	3,486,954
Retained Earnings | As Previously Reported
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			3,663,539	3,580,641
Comprehensive income (loss):
Net income (loss)				164,556
Balance, ending		3,515,197		3,515,197
Retained Earnings | Revision
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			(28,392)	(23,497)
Comprehensive income (loss):
Net income (loss)				(4,746)
Balance, ending		(28,243)		(28,243)
Total Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			4,482,425	4,530,488
Comprehensive income (loss):
Net income (loss)			480,682	159,810
Total comprehensive income (loss)			665,664	90,443
Balance, ending	$ 2,760,660	4,378,751	2,760,660	4,378,751
Total Equity | As Previously Reported
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			4,510,817	4,553,985
Comprehensive income (loss):
Net income (loss)				164,556
Total comprehensive income (loss)				95,189
Balance, ending		4,406,994		4,406,994
Total Equity | Revision
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning			$ (28,392)	(23,497)
Comprehensive income (loss):
Net income (loss)				(4,746)
Total comprehensive income (loss)				(4,746)
Balance, ending		$ (28,243)		$ (28,243)