Earnings per Limited Partner Unit or Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								6 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Mar. 31, 2013	Mar. 31, 2012
Basic and diluted earnings per common or subordinated unit:
Net income attributable to parent equity	$ 22,341	$ 40,176	$ 10,073	$ (24,650)	$ 13,954	$ 6,090	$ (5,395)	$ (6,773)	$ 12,679	$ 47,940	$ 7,876
Less - income allocated to general partner									(13)	(2,917)	(8)
NET INCOME (LOSS) ATTRIBUTABLE TO PARENT EQUITY ALLOCATED TO LIMITED PARTNERS									12,666	45,023	7,868
Common unitholders
Basic and diluted earnings per common or subordinated unit:
NET INCOME (LOSS) ATTRIBUTABLE TO PARENT EQUITY ALLOCATED TO LIMITED PARTNERS									12,666	39,517	4,859
Weighted average units outstanding (in shares)	47,665,015	46,364,381	44,831,836	26,529,133	23,263,386	18,699,590	8,864,222	9,883,342	10,933,568	41,353,574	15,169,983
Earnings per unit - basic and diluted:
Earnings per unit - basic and diluted (in dollars per share)									$ 1.16	$ 0.96	$ 0.32
Subordinated unitholders
Basic and diluted earnings per common or subordinated unit:
NET INCOME (LOSS) ATTRIBUTABLE TO PARENT EQUITY ALLOCATED TO LIMITED PARTNERS										$ 5,506	$ 3,009
Weighted average units outstanding (in shares)	5,919,346	5,919,346	5,919,346	5,919,346	5,919,346	5,919,346	5,199,346	2,927,149		5,919,346	5,175,384
Earnings per unit - basic and diluted:
Earnings per unit - basic and diluted (in dollars per share)										$ 0.93	$ 0.58