Partners' Capital, Equity and Incentive Compensation Plans (Schedule of Quarterly Cash Dividends) (Details) - USD ($) $ / shares in Units, $ in Thousands																				1 Months Ended	3 Months Ended				4 Months Ended	9 Months Ended
	Nov. 08, 2019	Oct. 15, 2019	Oct. 04, 2019	Sep. 30, 2019	Jun. 30, 2019	Jun. 25, 2019	Mar. 31, 2019	Mar. 20, 2019	Dec. 31, 2018	Dec. 21, 2018	Jun. 29, 2018	Jun. 25, 2018	Jun. 22, 2018	Jun. 20, 2018	Apr. 16, 2018	Apr. 05, 2018	Mar. 22, 2018	Mar. 15, 2018	Dec. 05, 2017	Feb. 28, 2019	Sep. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Oct. 31, 2018	Sep. 30, 2019	Sep. 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			$ 407,616
Preferred stock dividends per share cash paid															$ 0.14844
Preferred stock redemption price per share				$ 25.00																	$ 25.00					$ 25.00
Threshold period of redemption of preferred stock																										120 days
Ownership interest				50.00%																	50.00%					50.00%
Convertible preferred stock par value				$ 0.01																	$ 0.01					$ 0.01
Preferred stock, liquidation preference				25.00														$ 25.00			25.00					25.00
Share cap price				1.46929																	1.46929					$ 1.46929
Net proceeds																										$ 268,392
Preferred Units, Issued																		4,280,000
Series A Preferred Stock
Record Date					Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Jun. 29, 2018					Apr. 05, 2018
Payment Date					Jul. 15, 2019		Apr. 15, 2019		Jan. 15, 2019		Jul. 16, 2018					Apr. 16, 2018
Per Common Share and Per Unit Rate					$ 0.45		$ 0.45		$ 0.45		$ 0.45					$ 0.15
Dividend/Distribution Amount					$ 1,900		$ 1,900		$ 1,900		$ 1,900					$ 600										5,700	2,500
Series B Preferred Stock
Record Date					Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018
Payment Date					Jul. 15, 2019		Apr. 15, 2019		Jan. 15, 2019
Per Common Share and Per Unit Rate					$ 1.63		$ 1.63		$ 1.63
Dividend/Distribution Amount					$ 5,100		$ 5,100		$ 5,100																	$ 15,300
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																	$ 5.1020					$ 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		Sep. 30, 2019
Per Common Share and Per Unit Rate		$ 0.45
Subsequent Event | Series B Convertible preferred stock [Member]
Record Date		Sep. 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
At Market
Common Stock, Number Of Shares Authorized Under The Program																					1,200,000					1,200,000
Weighted Average Net Price Per Share																					$ 49					$ 49
Forward Sales Provision [Member] | Class A Common Stock
Weighted Average Net Price Per Share	$ 51
Shares issued	2,800,000
The amount of common stock available for sale	$ 258,000																									$ 343,000
Net proceeds	$ 139,000			$ 56,000
Proceeds from stock remaining available for sale																						$ 36,000				175,000
Underwritten Offering | Class A Common Stock
Share price																				$ 41.50
Shares issued																				900,000	2,800,000	4,000,000
Net proceeds																					$ 110,000	$ 159,000
Proceeds from stock remaining available for sale																					$ 36,000
Qualitytech, LP
Preferred stock issuance proceeds, net of costs																											407,616
Net proceeds																										268,392
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						Jun. 25, 2019		Mar. 20, 2019		Dec. 21, 2018				Jun. 20, 2018			Mar. 22, 2018		Dec. 05, 2017
Payment Date						Jul. 09, 2019		Apr. 04, 2019		Jan. 08, 2019				Jul. 06, 2018			Apr. 05, 2018		Jan. 05, 2018
Per Common Share and Per Unit Rate						$ 0.44		$ 0.44		$ 0.41				$ 0.41			$ 0.41		$ 0.39
Dividend/Distribution Amount						$ 27,300		$ 27,300		$ 23,700				$ 23,700			$ 23,700		$ 22,200							$ 78,300	$ 69,600
Shares issued																						4,000,000
Common stock | Subsequent Event
Record Date			Sep. 19, 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
Preferred stock | Series A Preferred Stock
Shares issued																								4,280,000
Preferred stock | Series B Preferred Stock
Shares issued																							3,163,000