Members' Equity (Details 2) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended							12 Months Ended
	Apr. 02, 2011 item	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2014 Phantom Units	Mar. 31, 2013 Phantom Units	Mar. 31, 2012 Phantom Units	Apr. 02, 2013 Phantom Units	Mar. 31, 2014 Phantom Units Phantom Units Outstanding	Mar. 31, 2014 Phantom Units Nonvested Phantom Units	Mar. 31, 2014 Time-based phantom units Phantom Units Outstanding	Mar. 31, 2014 Time-based phantom units Nonvested Phantom Units	Mar. 31, 2014 Performance-Based phantom units Phantom Units Outstanding	Mar. 31, 2014 Performance-Based phantom units Nonvested Phantom Units
Members Equity
Period over which phantom units vest					3 years
Number of compensatory PUPP plans	2
Number of units authorized under the PUPP (in shares)					3,380,474
Weighted average price of granted units (in dollars per share)					$ 12.68	$ 9.99	$ 21.95
Number of units available for grant (in shares)					1,483,708	2,045,693		2,045,693
Reconciliation of Phantom Units Outstanding
Balance at the beginning of the period (in shares)									932,007	809,011	624,518	563,020	307,489	245,991
Granted (in shares)					438,036	695,349	518,425		438,036	438,036	219,018	219,018	219,018	219,018
Vested (in shares)										(542,938)		(368,502)		(174,436)
Exercised (in shares)									(122,996)		(61,498)		(61,498)
Forfeited (in shares)									(48,437)	(48,437)	(24,718)	(24,718)	(23,719)	(23,719)
Distribution equivalent rights (in shares)									123,950	123,950	78,040	78,040	45,910	45,910
Balance at the end of the period (in shares)									1,322,560	779,622	835,360	466,858	487,200	312,764
Additional disclosures
Total unrecognized compensation cost										$ 5.9
Period for expected unrecognized compensation cost to be recognized										2 years
Unit-based compensation costs		11.2	7.0	0.5
Cash paid to employees who exercised Phantom Units					$ 2.3	$ 0	$ 0