Distributions and Net Income Per Limited Partner Unit (Basic and Diluted Income Per Limited Partner Unit) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,591	$ 16,348	$ 49,772	$ 48,127
Net income in excess of distribution (distribution in excess of net income)	1,944	(1,426)	1,370	(4,517)
Net income	$ 18,535	$ 14,922	$ 51,142	$ 43,610
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	35,188,189	35,194,545	34,251,005
Common units [Member]
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 16,591	$ 16,348	$ 49,772	$ 48,127
Net income in excess of distribution (distribution in excess of net income)	1,944	(1,426)	1,370	(4,517)
Net income	$ 18,535	$ 14,922	$ 51,142	$ 43,610
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted	35,194,545	35,188,189	35,194,545	34,251,005
Weighted average units outsanding:
Net Income (Loss), Per Outstanding Limited Partnership Unit, Basic, Net of Tax	$ 0.53	$ 0.42	$ 1.45	$ 1.27
IDR Holders [Member]
Limited Partners' Capital Account [Line Items]
Subsequent distribution to IDR holders	$ 0	$ 0	$ 0	$ 0
Net income in excess of distribution (distribution in excess of net income)	0	0	0	0
Net income	$ 0	$ 0	$ 0	$ 0