Equity (Distributions) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended					9 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 61,767
Incentive Distribution, Distribution		$ 1,175			$ 326	2,857	$ 481
Distribution Made to Limited Partner, Cash Distributions Paid		21,322			17,092	58,910	48,924
Partners' Capital Account, Distributions		$ 22,497			$ 17,418	$ 62,077	$ 49,405
Distribution Made to Limited Partner, Distributions Declared, Per Unit		$ 0.4125	$ 0.4025	$ 0.3925	$ 0.3650	$ 1.2075	$ 1.0450
Subsequent Event [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.4225							$ 1.6300
TexNew Mex Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared						$ 0
Distribution Made to Limited Partner, Cash Distributions Paid		$ 0			$ 0	310	$ 0
Common Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared		11,913			8,766	31,366	25,086
Distribution Made to Limited Partner, Cash Distributions Paid		11,913			8,766	31,366	25,086
Subordinated Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared		9,409			8,326	27,544	23,838
Distribution Made to Limited Partner, Cash Distributions Paid		$ 9,409			$ 8,326	$ 27,544	$ 23,838