Income Taxes (Recognized Income Tax Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Federal:
Current	$ (4,638)	$ 2,507	$ 2,642
Deferred	24,121	46,089	47,909
Total federal income tax	19,483	48,596	50,551
State:
Current	1,888	(897)	766
Deferred	1,941	1,816	3,285
Total state income tax	3,829	919	4,051
Generation (amortization) of accumulated investment tax credits	3,056	1,489	(684)
Total income tax expense	$ 26,368	$ 51,004	$ 53,918