Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements of Comprehensive Income [Abstract]
Unrealized investment gains (losses) arising during the period, net of tax expense (benefit)	$ (36)	$ 82	$ 137
Amortization of net actuarial loss, net of tax expense (benefit)	(709)	1,433	(2,859)
Amortization of prior service credit, net of tax	$ 487	$ 17	$ 353