Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Comprehensive Income [Abstract]
Unrealized investment gains (losses) arising during the period, net of tax expense (benefit)	$ 33	$ (36)	$ 82
Amortization of net actuarial loss, net of tax expense (benefit)	(574)	(709)	1,433
Amortization of prior service credit, net of tax	$ (433)	$ (487)	$ 17