Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Partners' Capital [Abstract]
Net Income	$ 32,787	$ 28,863	$ 27,622
Employee Benefits, net of tax:
Amortization of prior service cost, net of tax of ($24), ($26) and $432, respectively	(36)	(37)	645
Net gain (loss), net of tax of $1,673, ($331) and ($1,164), respectively	2,565	(498)	(1,812)
Total other comprehensive income (loss)	2,529	(535)	(1,167)
Comprehensive Income	$ 35,316	$ 28,328	$ 26,455