Summary of Significant Accounting Policies (Prepaid Expenses and Other) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Prepaid expense
Prepaid expenses	$ 4,168	$ 5,275
California carbon allowance inventories	545	0
Oil inventories	1,216	0
Materials inventories	12,943	11,356
Other inventory	193	170
Total prepaid expenses and other	$ 19,065	$ 16,801