Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income for common stock	$ 45,927	$ 33,679
Net unrealized gains (losses) on securities:
Net unrealized gains (losses) on securities arising during the period, net of (taxes) benefits of ($1,664) and $547 for the respective periods	2,520	(828)
Less: reclassification adjustment for net realized gains included in net income, net of taxes of $1,132 and nil for the respective periods	(1,715)	0
Derivatives qualified as cash flow hedges:
Less: reclassification adjustment to net income, net of tax benefits of $37 for both periods	59	59
Retirement benefit plans:
Less: amortization of transition obligation, prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $1,796 and $3,846 for the respective periods	2,813	6,021
Less: reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of taxes of $1,598 and $3,384 for the respective periods	(2,510)	(5,313)
Other comprehensive income (loss), net of taxes	1,167	(61)
Comprehensive income	$ 47,094	$ 33,618