Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Tax expense recognized on the amortization of prior service cost	$ (26)	$ 432	$ 5
Tax expense recognized on the net gain (loss)	$ (331)	$ (1,164)	$ (541)