Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Partners' Capital [Abstract]
Tax expense recognized on the amortization of prior service cost	$ (24)	$ (26)	$ 432
Tax expense recognized on the net gain (loss)	$ 1,673	$ (331)	$ (1,164)