Condensed Consolidated Statements Of Partners' Capital (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Partners' Capital Account, Sale of Units	$ 225,610,000	$ 263,597,000
Partners' capital, January 1, units	88,690,985	81,202,752
Partners' capital, January 1, value	1,097,737,000	916,495,000
Net income	80,036,000	68,222,000
Cash distributions	146,350,000	122,097,000
Partners' Capital Account, Exchanges and Conversions	0	0
Partners' capital, September 30, units	93,290,985	88,691,000
Partners' capital, September 30, value	1,257,033,000	1,126,217,000
Number Of Common Units [Member]
Net income	0	0
Cash distributions	$ 0	$ 0
Partners' Capital Account, Units, Sale of Units	4,600,000	5,750,000
Partners' Capital Account, Units, Converted	0	1,738,000