Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Decrease in estimated fair value of investment in debt securities, tax	$ (1,162)	$ 1,710	$ 1,004
Unrecognized actuarial loss and prior service cost, income taxes	(699)	(10,293)	(3,116)
Income tax on cash flow hedge activity	$ 66	$ (21)	$ (112)