Income Taxes Domestic Tax Components (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Federal
Current	$ 5,358	$ (159)	$ 1,529
Deferred	13,197	18,618	23,322
Investment tax credits	(376)	(424)	(427)
State
Current	(1,411)	(27)	7
Deferred	1,321	(7,943)	1,329
Total income tax expense	$ 18,089	$ 10,065	$ 25,760