Equity and Capital - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Document Fiscal Year Focus	2015
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 9,152	$ 9,353	$ 9,433
Weighted Average Limited Partnership Units Outstanding, Basic	154,170	157,950	171,886
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 9,152	$ 9,353	$ 9,433
Accumulated Net Realized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(7,765)	0
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(10,132)	(42,203)	30,985
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	9,152	1,588	9,433
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(58,498)	(17,883)	(58,301)
Current period other comprehensive income, net	(980)	(40,615)	40,418
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(59,478)	(58,498)	(17,883)
Parent Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	7,765	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(57,748)
Current period other comprehensive income, net	(980)	(40,615)	40,418
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(58,693)	(57,748)
Parent Company [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Current period other comprehensive income, net	(945)	(40,344)	40,311
Noncontrolling Interest [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(192)	(444)	106
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	157	173	1
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(750)	(479)	(586)
Current period other comprehensive income, net	(35)	(271)	107
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(785)	(750)	(479)
Noncontrolling Interest [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	0	13	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(13)	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	0	0	0
Current period other comprehensive income, net	0	0	0
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	0	0	0
Noncontrolling Interest [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(192)	(431)	106
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	157	160	1
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(750)	(479)	(586)
Current period other comprehensive income, net	(35)	(271)	107
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(785)	(750)	(479)
Controlling [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(9,897)	(49,524)	30,879
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	8,995	9,180	9,432
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(57,748)	(17,404)	(57,715)
Current period other comprehensive income, net	(902)	(40,344)	40,311
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(58,650)	(57,748)	(17,404)
Controlling [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(43)	7,752	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(7,752)	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	0	0	0
Current period other comprehensive income, net	(43)	0	0
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	(43)	0	0
Controlling [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(9,940)	(41,772)	30,879
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	8,995	1,428	9,432
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning of Period	(57,748)	(17,404)	(57,715)
Current period other comprehensive income, net	(945)	(40,344)	40,311
Accumulated Other Comprehensive Income (Loss), Net of Tax, End of Period	$ (58,693)	$ (57,748)	$ (17,404)