Capital and Accumulated Other Comprehensive Income (Loss) Capital and Accumulated Other Comprehensive Income (Loss) (Redeemable Preferred Units) (Details) - USD ($)								12 Months Ended
	Sep. 14, 2017	Aug. 07, 2017	Apr. 05, 2017	Aug. 24, 2015	Mar. 26, 2014	Apr. 09, 2013	Apr. 05, 2012	Dec. 31, 2017	Dec. 31, 2016
Preferred Units [Line Items]
Total liquidation value								$ 1,448,750,000
Units outstanding as of December 31								50,650,000	41,900,000
Balance (in thousands, net of issuance costs) as of December 31,								$ 1,249,560,000	$ 1,012,961,000
Preferred Stock, liquidation preference per share/unit (in dollars per unit)								$ 25.00
Series C Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 201,250,000
Annual rate of dividend per share (in dollars per share)	$ 1.65625
Units outstanding as of December 31								8,050,000	0
Balance (in thousands, net of issuance costs) as of December 31,								$ 219,250,000	$ 0
Series F Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 182,500,000
Annual rate of dividend per share (in dollars per share)							$ 1.65625
Units outstanding as of December 31								0	7,300,000
Balance (in thousands, net of issuance costs) as of December 31,								$ 0	$ 176,191,000
Preferred stock, redemption price per share (in dollars per unit)			$ 25.01840
Accrued and unpaid dividends up to but not including the redemption date			$ 100,000
Redemption premium			$ 6,300,000
Series G Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 250,000,000
Annual rate of dividend per share (in dollars per share)						$ 1.46875
Units outstanding as of December 31								10,000,000	10,000,000
Balance (in thousands, net of issuance costs) as of December 31,								$ 241,468,000	$ 241,468,000
Series H Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 365,000,000
Annual rate of dividend per share (in dollars per share)					$ 1.84375
Units outstanding as of December 31								14,600,000	14,600,000
Balance (in thousands, net of issuance costs) as of December 31,								$ 353,290,000	$ 353,290,000
Series I Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 250,000,000
Annual rate of dividend per share (in dollars per share)				$ 1.58750
Units outstanding as of December 31								10,000,000	10,000,000
Balance (in thousands, net of issuance costs) as of December 31,								$ 242,012,000	$ 242,012,000
Series J Preferred Units
Preferred Units [Line Items]
Total liquidation value								$ 200,000,000
Annual rate of dividend per share (in dollars per share)		$ 1.31250
Units outstanding as of December 31								8,000,000	0
Balance (in thousands, net of issuance costs) as of December 31,								$ 193,540,000	$ 0