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
Mar. 31, 2019	Mar. 31, 2018
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 15,666	$ 13,547
Net income in excess of distribution (distribution in excess of net income)	(711)	(1,252)
Net income	$ 14,955	$ 12,295
Weighted average units outsanding:
Basic and diluted (shares)	32,345,398	32,236,449
Common units [Member]
Limited Partners' Capital Account [Line Items]
Distributions declared	$ 15,666	$ 12,814
Net income in excess of distribution (distribution in excess of net income)	(711)	(1,252)
Net income	$ 14,955	$ 11,562
Weighted average units outsanding:
Basic and diluted (shares)	32,345,398	32,236,449
Net income per limited partner unit:
Income per limited partner unit (usd per share)	$ 0.46	$ 0.36
IDR Holders [Member]
Limited Partners' Capital Account [Line Items]
Subsequent distribution to IDR holders	$ 0	$ 733
Net income in excess of distribution (distribution in excess of net income)	0	0
Net income	$ 0	$ 733

The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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