Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Accounting Policies [Abstract]

Prepaid Expenses and Other

	Year Ended December 31,
(in thousands)	2012		2011
Prepaid expenses	$	4,168	$	5,275
California carbon allowance inventories	545		—
Oil inventories	1,216		—
Materials inventories	12,943		11,356
Other inventory	193		170
Total prepaid expenses and other	$	19,065	$	16,801

Schedule of Accrued Liabilities

	Year Ended December 31,
(in thousands)	2012		2011
Property taxes	$	13,496	$	10,430
Accrued interest	16,996		9,205
Accrued payroll	12,700		9,953
Asset retirement obligations (current portion)	4,430		4,763
Other accrued liabilities	3,529		5,478
Total accrued liabilities	$	51,151	$	39,829

Computation of Basic and Diluted Earnings (Loss) Per Share

	Year Ended December 31,
(in thousands, except per share data)	2012		2011			2010
Net earnings (loss)	$	171,539	$	(228,063	)	$	82,524
Less: Earnings allocable to participating securities	885		—			1,199
Net earnings (loss) available for common shareholders	$	170,654	$	(228,063	)	$	81,325
Basic net earnings (loss) per share	$	3.11	$	(4.21	)	$	1.54
Diluted net earnings (loss) per share	$	3.09	$	(4.21	)	$	1.52
Basic weighted average shares outstanding	54,912		54,133			52,969
Add: Dilutive effects of stock options and RSUs	375		—			460
Diluted weighted average shares outstanding	55,287		54,133			53,429

Revenue from External Customers by Products and Services [Table Text Block]

	Year Ended December 31,
	2012		2011		2010
Oil and natural gas:
ExxonMobil Oil Corporation	43	%	43	%	44	%
Shell Trading (US) Company	13	%	14	%	14	%
Enterprise Crude Oil LLC	9	%	8	%	4	%
HollyFrontier Corporation	9	%	8	%	9	%
Electricity:
Pacific Gas and Electric Company	54	%	59	%	55	%
Southern California Edison	46	%	41	%	45	%