Management's Statement: Correction of Immaterial Errors (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Statement [Abstract]
Depreciation, depletion and amortization	$ 40,051	$ 35,877	$ 79,053	$ 71,126
Total operating expenses	311,112	235,825	682,599	605,562
Operating income (loss)	(38,858)	47,412	31,642	137,844
Income (loss) before earnings (loss) of unconsolidated subsidiaries and income taxes	(56,942)	31,306	(5,083)	105,624
Income tax expense (benefit)	20,317	(10,959)	2,605	(36,632)
Net income (loss) available for common stock	$ (41,842)	$ 20,347	$ (7,992)	$ 68,992
Total income (loss) per share, Basic	$ (0.94)	$ 0.46	$ (0.18)	$ 1.56
Total income (loss) per share, Diluted	$ (0.94)	$ 0.46	$ (0.18)	$ 1.55
Comprehensive income (loss)	$ (44,647)	$ 19,495	$ (9,807)	$ 66,973
Balance Sheet [Abstract]
Accumulated depreciation and depletion	(1,522,969)	(1,361,233)	(1,522,969)	(1,361,233)	$ (1,357,929)
Total property, plant and equipment, net	3,203,509	3,047,058	3,203,509	3,047,058	3,205,471
Total Assets	4,220,271	3,934,925	4,220,271	3,934,925	4,245,902
Deferred income tax liabilities, net, non-current	510,435	463,680	510,435	463,680	511,952
Total deferred credits and other liabilities	983,150	841,561	983,150	841,561	973,148
Retained earnings	532,965	550,185	532,965	550,185	577,249
Total stockholders’ equity	1,310,886	1,318,131	1,310,886	1,318,131	1,353,884
Total Liabilities and Stockholders' Equity	$ 4,220,271	3,934,925	4,220,271	3,934,925	$ 4,245,902
Statement of Cash Flows [Abstract]
Net Cash Provided by (Used in) Operating Activities			254,408	173,835
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Deferred income taxes			$ (6,277)	36,129
Scenario, Previously Reported [Member]
Income Statement [Abstract]
Depreciation, depletion and amortization		36,712		72,795
Total operating expenses		236,660		607,231
Operating income (loss)		46,577		136,175
Income (loss) before earnings (loss) of unconsolidated subsidiaries and income taxes		30,471		103,955
Income tax expense (benefit)		(10,651)		(36,017)
Net income (loss) available for common stock		$ 19,820		$ 67,938
Total income (loss) per share, Basic		$ 0.45		$ 1.53
Total income (loss) per share, Diluted		$ 0.44		$ 1.52
Comprehensive income (loss)		$ 18,968		$ 65,919
Balance Sheet [Abstract]
Accumulated depreciation and depletion		(1,325,660)		(1,325,660)
Total property, plant and equipment, net		3,082,631		3,082,631
Total Assets		3,970,498		3,970,498
Deferred income tax liabilities, net, non-current		476,059		476,059
Total deferred credits and other liabilities		853,940		853,940
Retained earnings		573,379		573,379
Total stockholders’ equity		1,341,325		1,341,325
Total Liabilities and Stockholders' Equity		3,970,498		3,970,498
Statement of Cash Flows [Abstract]
Net Cash Provided by (Used in) Operating Activities				173,835
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Deferred income taxes				35,514
Scenario, Adjustment [Member]
Income Statement [Abstract]
Depreciation, depletion and amortization		(835)		(1,669)
Total operating expenses		(835)		(1,669)
Operating income (loss)		835		1,669
Income (loss) before earnings (loss) of unconsolidated subsidiaries and income taxes		835		1,669
Income tax expense (benefit)		(308)		(615)
Net income (loss) available for common stock		$ 527		$ 1,054
Total income (loss) per share, Basic		$ 0.01		$ 0.03
Total income (loss) per share, Diluted		$ 0.02		$ 0.03
Comprehensive income (loss)		$ 527		$ 1,054
Balance Sheet [Abstract]
Accumulated depreciation and depletion		(35,573)		(35,573)
Total property, plant and equipment, net		(35,573)		(35,573)
Total Assets		(35,573)		(35,573)
Deferred income tax liabilities, net, non-current		(12,379)		(12,379)
Total deferred credits and other liabilities		(12,379)		(12,379)
Retained earnings		(23,194)		(23,194)
Total stockholders’ equity		(23,194)		(23,194)
Total Liabilities and Stockholders' Equity		$ (35,573)		(35,573)
Statement of Cash Flows [Abstract]
Net Cash Provided by (Used in) Operating Activities				0
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Deferred income taxes				$ 615