Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Unrealized (losses) gains on marketable securities arising during period, tax	$ 216	$ 370	$ 1,247
Reclassification adjustment for gains included in net income, tax	(257)	(201)	(581)
Amortization of prior service (benefit) costs, tax	$ (159)	$ (134)	$ 9