Partners' Capital, Equity and Incentive Compensation Plans (Schedule of Quarterly Cash Dividends) (Details) - USD ($) $ / shares in Units, $ in Thousands									3 Months Ended		4 Months Ended	12 Months Ended
	Apr. 04, 2019	Mar. 20, 2019	Dec. 21, 2018	Jun. 25, 2018	Jun. 22, 2018	Apr. 16, 2018	Mar. 15, 2018	Dec. 05, 2017	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2018	Dec. 31, 2018
Record Date		Mar. 20, 2019
Partnership distribution per unit	$ 0.44
Dividend rate (as a percent)							7.125%
Preferred stock, shares issued							4,280,000
Preferred stock issuance proceeds, net of costs										$ 103,615
Preferred stock dividends per share cash paid						$ 0.14844
Preferred stock redemption price per share									$ 25.00
Threshold period of redemption of preferred stock									120 days
Ownership interest									50.00%
Convertible preferred stock par value									$ 0.01
Preferred stock, liquidation preference							$ 25.00		25.00
Share cap price									$ 1.46929
Series A Preferred Stock
Record Date												Dec. 31, 2018
Payment Date												Jan. 15, 2019
Per Common Share and Per Unit Rate												$ 0.45
Dividend/Distribution Amount									$ 1,900			$ 1,900
Series B Preferred Stock
Record Date												Dec. 31, 2018
Payment Date												Jan. 15, 2019
Per Common Share and Per Unit Rate												$ 1.63
Dividend/Distribution Amount									$ 5,100			$ 5,100
Series A Redeemable Perpetual Preferred
Per Common Share and Per Unit Rate									$ 0.45
Series B Convertible preferred stock [Member]
Per Common Share and Per Unit Rate									$ 1.63
Dividend rate (as a percent)				6.50%	6.50%
Preferred stock, shares issued				3,162,500
Preferred stock issuance proceeds, net of costs				$ 304,000
Minimum percentage of closing sale price of common stock under preferred stock conversion (as a percent)									2.1278%
Minimum trading days of closing sale price of common stock under preferred stock conversion (in days)									20 years
Maximum trading days of closing sale price of common stock under preferred stock conversion including the last trading day (in days)									30 days
Preferred stock dividends per share cash paid											$ 1.9861111
Preferred stock, liquidation preference				$ 100.00
Period of average daily volume weighted average price									10 years
Share cap price									$ 5.1020
Series B Convertible preferred stock [Member] | Minimum
Minimum percentage of closing sale price of common stock under preferred stock conversion (as a percent)									150.00%
Underwriter's Option
Preferred stock, shares issued							280,000
Underwriter's Option | Series B Convertible preferred stock [Member]
Preferred stock, shares issued				412,500
Common stock
Record Date			Dec. 21, 2018					Dec. 05, 2017
Payment Date			Jan. 08, 2019					Jan. 05, 2018
Per Common Share and Per Unit Rate			$ 0.41					$ 0.39
Dividend/Distribution Amount			$ 23,700					$ 22,200	$ 23,700	$ 22,200
Common stock | Subsequent Event
Per Common Share and Per Unit Rate	$ 0.44