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	6 Months Ended
	Jul. 15, 2019	Jul. 09, 2019	Mar. 31, 2019	Mar. 20, 2019	Dec. 31, 2018	Dec. 21, 2018	Jun. 25, 2018	Jun. 22, 2018	Apr. 16, 2018	Apr. 05, 2018	Mar. 22, 2018	Mar. 15, 2018	Dec. 05, 2017	Mar. 31, 2018	Oct. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 26, 2018
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														$ 103,200			$ 408,415
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			Mar. 31, 2019		Dec. 31, 2018					Apr. 05, 2018
Payment Date			Apr. 15, 2019		Jan. 15, 2019					Apr. 16, 2018
Per Common Share and Per Unit Rate			$ 0.45		$ 0.45					$ 0.15
Dividend/Distribution Amount			$ 1,900		$ 1,900					$ 600						$ 3,800	600
Series B Preferred Stock
Record Date			Mar. 31, 2019		Dec. 31, 2018
Payment Date			Apr. 15, 2019		Jan. 15, 2019
Per Common Share and Per Unit Rate			$ 1.63		$ 1.63
Dividend/Distribution Amount			$ 5,100		$ 5,100											$ 10,300
Series B Convertible preferred stock
Preferred stock, shares issued																		3,162,500
Minimum trading days of closing sale price of common stock under preferred stock conversion (in days)																20 days
Period of average daily volume weighted average price																10 days
Series B Convertible preferred stock [Member]
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)																2.1279%
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
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%
Subsequent Event | Series A Redeemable Perpetual Preferred
Record Date	Jun. 30, 2019
Per Common Share and Per Unit Rate	$ 0.45
Subsequent Event | Series B Convertible preferred stock [Member]
Record Date	Jun. 30, 2019
Per Common Share and Per Unit Rate	$ 1.63
Underwriter's Option
Preferred stock, shares issued												280,000
Underwriter's Option | Series B Convertible preferred stock [Member]
Preferred stock, shares issued							412,500
Qualitytech, LP
Preferred stock issuance proceeds, net of costs																	408,415
Qualitytech, LP | Subsequent Event | Series A Redeemable Perpetual Preferred
Per Common Share and Per Unit Rate	0.45
Qualitytech, LP | Subsequent Event | Series B Convertible preferred stock
Per Common Share and Per Unit Rate	$ 1.63
Common stock
Record Date				Mar. 20, 2019		Dec. 21, 2018					Mar. 22, 2018		Dec. 05, 2017
Payment Date				Apr. 04, 2019		Jan. 08, 2019					Apr. 05, 2018		Jan. 05, 2018
Per Common Share and Per Unit Rate				$ 0.44		$ 0.41					$ 0.41		$ 0.39
Dividend/Distribution Amount				$ 27,300		$ 23,700					$ 23,700		$ 22,200			$ 51,000	$ 45,900
Common stock | Subsequent Event
Record Date		Jun. 25, 2019
Per Common Share and Per Unit Rate		$ 0.44
Common stock | Qualitytech, LP | Subsequent Event
Per Common Share and Per Unit Rate		$ 0.44