Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Contingency
Deferred Tax Liabilities, Net, Current	$ 1,456,000	$ 0
Deferred Tax Liabilities, Gross	307,136,000	220,656,000
Deferred income taxes	703,000	13,779,000
Deferred income taxes, noncurrent	255,471,000	185,450,000
Unrecognized Tax Benefits Maximum Estimated Reductions Resulting from Expiration of Applicable Statute of Limitations in Next 12 Months	6,700,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense		500,000	100,000
Unrecognized tax benefit, if recognized, would affect the effective tax rate	17,500,000
Accrued interest recognized due to uncertain tax positions	400,000	800,000
Unrecognized Tax Benefits, Reversal of Interest Expense	(400,000)
Deferred Tax Assets, Valuation Allowance	1,201,000	403,000
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	800,000	0	100,000
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions			800,000
Increases (decreases) for positions taken in a prior year	20,500,000	0
Federal and State
Income Tax Contingency
Deferred Tax Liabilities, Net, Current	800,000
Deferred income taxes		13,779,000
Deferred income taxes, noncurrent	255,471,000	185,450,000
California | State
Income Tax Contingency
Deferred Tax Assets, Tax Credit Carryforwards, Research		18,300,000
Tax credit carryforwards, alternative minimum tax	600,000
California | EOR tax credit | State
Income Tax Contingency
Tax credit carryforwards	12,500,000
UNITED STATES | Federal
Income Tax Contingency
Deferred Tax Assets, Tax Credit Carryforwards, Research	10,400,000
Tax credit carryforwards, alternative minimum tax	800,000
UNITED STATES | EOR tax credit | Federal
Income Tax Contingency
Tax credit carryforwards	10,600,000
COLORADO | Enterprise zone income tax credits | State
Income Tax Contingency
Tax credit carryforwards	$ 3,000,000