Partners' Capital and Distributions (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended										12 Months Ended				0 Months Ended					12 Months Ended				1 Months Ended
	Sep. 16, 2013	Mar. 28, 2012	Jul. 31, 2011	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 Waiver Units Class1 [Member]	Dec. 31, 2013 Waiver Units Class 2 [Member]	Dec. 31, 2013 Waiver Units Class 3 [Member]	Dec. 31, 2013 Waiver Units Class4 [Member]	Sep. 16, 2013 Class A [Member]	Mar. 28, 2012 Class A [Member]	Dec. 31, 2013 Class A [Member]	Feb. 01, 2012 Class A [Member]	Dec. 31, 2013 Class B [Member]	Dec. 31, 2013 Waiver Units [Member]	Dec. 31, 2013 Class Two [Member]	Dec. 31, 2013 Class Three [Member]	Dec. 31, 2013 Class Four [Member]	Jul. 31, 2011 FMT Black Oil Barge Transportation Business [Member] Class A [Member]
Partners Capital And Distributions [Line Items]
Common units, outstanding				88,690,985	88,690,985	81,202,752															88,650,988		39,997
Waiver units authorized															1,738,000	1,738,000	1,738,000	1,738,000						1,738,233
Conversion feature, minimum distribution coverage ratio					1.1																				1.1	1.1	1.1
Conversion feature threshold, quarterly distribution, minimum, per unit																										0.49	0.52
Waiver Units Class 3 Convertible Date				May 15, 2013
Per Unit Amount				$ 0.5225	$ 0.5225	$ 0.4725		$ 0.5350	$ 0.5100	$ 0.4975	$ 0.4850	$ 0.4600	$ 0.4500	$ 0.4400												$ 0.4975
Limited Partners' ownership percentage					100.00%
Number of common units issued	5,750,000			88,690,985	88,690,985	81,202,752																5,750,000						7,350,000
Cash or stock available for distributions, percent usually distributed					100.00%
Days to distribute					45 days
Price per share of common units issued	$ 47.51	$ 30.80	$ 26.30						$ 0											$ 30.80
Proceeds received from offering, net of costs	$ 263,574	$ 169,421	$ 184,969																$ 263,600	$ 169,400								$ 185,000
Issuance of common units for cash, net					$ 263,574	$ 169,421	$ 184,969