Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net unrealized gains (losses) on available-for-sale investment securities arising during the period, net of tax benefits	$ 2,278	$ 1,664
Less: reclassification adjustment for net realized gains included in net income, net of tax benefits	0	1,132
Less: reclassification adjustment to net income, net of tax benefits	(37)	(37)
Less: amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits	(3,486)	(1,796)
Less: reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of tax benefits	$ (3,127)	$ (1,598)