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Distributions and Net Income Per Limited Partner Unit (Distributions Declared) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Distribution Made to Limited Partner [Line Items]
Net income attributable to the Partnership		$ 14,955	$ 12,295
Distributions declared		15,666	13,547
Net income in excess of distribution (distribution in excess of net income)		$ (711)	$ (1,252)
Weighted average limited partner units outstanding (basic and diluted) (in shares)		32,345,398	32,236,449
IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Net income attributable to the Partnership		$ 0	$ 733
Distributions declared with respect to the incentive distribution rights		0	733
Net income in excess of distribution (distribution in excess of net income)		0	0
Common units [Member]
Distribution Made to Limited Partner [Line Items]
Net income attributable to the Partnership		14,955	11,562
Distributions declared		15,666	12,814
Net income in excess of distribution (distribution in excess of net income)		$ (711)	$ (1,252)
Weighted average limited partner units outstanding (basic and diluted) (in shares)		32,345,398	32,236,449
Income per limited partner unit (usd per share)		$ 0.46	$ 0.36
Cash Distribution [Member] \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Distributions declared with respect to the incentive distribution rights		$ 0	$ 733
Cash Distribution [Member] \| Common units [Member]
Distribution Made to Limited Partner [Line Items]
Distributions declared		$ 15,666	$ 12,814
Cash Distribution [Member] \| Common And Subordinated Units [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.2938
Cash Distribution [Member] \| Common And Subordinated Units [Member] \| Subsequent Event [Member]
Distribution Made to Limited Partner [Line Items]
Distribution declared per unit (in usd per unit)	$ 0.4452
Above $1.2938 up to $1.4063 \| Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		1.2938
Above $1.2938 up to $1.4063 \| Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.4063
Above $1.2938 up to $1.4063 \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		85.00%
Above $1.2938 up to $1.4063 \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		15.00%
Above $1.4063 up to $1.6875 \| Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.4063
Above $1.4063 up to $1.6875 \| Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.6875
Above $1.4063 up to $1.6875 \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		75.00%
Above $1.4063 up to $1.6875 \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		25.00%
Above $1.6875 \| Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution Rights, Target Distribution Per Unit Requiring Marginal Percentage Distribution to IDR Holders		$ 1.6875
Above $1.6875 \| Unit Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		50.00%
Above $1.6875 \| IDR Holders [Member]
Distribution Made to Limited Partner [Line Items]
Incentive Distribution, Marginal Percentage Interest in Distributions		50.00%