Fair Value of Financial Instruments (Schedule of Regression Coefficients utilized in Unobservable Input Adjustments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Minimum [Member] | Propane
Regression coefficient	0.8969		0.9019
Minimum [Member] | Isobutane
Regression coefficient	1.1274		1.1285
Minimum [Member] | Normal butane [Member]
Regression coefficient	1.0384		1.0370
Minimum [Member] | Natural Gasoline [Member]
Regression coefficient	0.9063		0.8988
Maximum [Member] | Propane
Regression coefficient	0.9069		0.9122
Maximum [Member] | Isobutane
Regression coefficient	1.1366		1.1376
Maximum [Member] | Normal butane [Member]
Regression coefficient	1.0430		1.0416
Maximum [Member] | Natural Gasoline [Member]
Regression coefficient	0.9251		0.9169
Weighted Average [Member] | Propane
Regression coefficient	0.9019		0.9071
Weighted Average [Member] | Isobutane
Regression coefficient	1.1320		1.1331
Weighted Average [Member] | Normal butane [Member]
Regression coefficient	1.0407		1.0393
Weighted Average [Member] | Natural Gasoline [Member]
Regression coefficient	0.9157		0.9078
Derivative Financial Instruments, Assets [Member] | Level 3 [Member]
Derivative, fair value asset (liability)	16,505		23,083
Derivative Financial Instruments, Assets [Member] | Level 3 [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	11,793		16,814
Derivative Financial Instruments, Assets [Member] | Adjustments [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	(2,372)	[1]	(1,607)	[1]
Derivative Financial Instruments, Assets [Member] | Propane | Level 3 [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	9,587		15,750
Derivative Financial Instruments, Assets [Member] | Propane | Adjustments [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	(319)	[1]	(552)	[1]
Derivative Financial Instruments, Assets [Member] | Isobutane | Level 3 [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	126		(32)
Derivative Financial Instruments, Assets [Member] | Isobutane | Adjustments [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	78	[1]	187	[1]
Derivative Financial Instruments, Assets [Member] | Normal butane [Member] | Level 3 [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	367		(667)
Derivative Financial Instruments, Assets [Member] | Normal butane [Member] | Adjustments [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	134	[1]	242	[1]
Derivative Financial Instruments, Assets [Member] | Natural Gasoline [Member] | Level 3 [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	1,713		1,763
Derivative Financial Instruments, Assets [Member] | Natural Gasoline [Member] | Adjustments [Member] | Commodity Swaps [Member]
Derivative, fair value asset (liability)	(2,265)	[1]	(1,484)	[1]

[1] Product and location basis differentials calculated through the use of a regression model, which compares the difference between the settlement prices for the products and locations quoted by the third party and the settlement prices for the actual products and locations underlying the derivatives, using a three year historical period.