Consolidated Statements of Changes in Capital - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Partners' Capital [Roll Forward]
Trust Restricted share award grants, net	$ 1,109					$ 2,228
Issuance of common shares in connection with the Ziegler shared service amendment payment									$ 1,800
Conversion of OP Units	0
Contributions							$ 50	$ 8,962
Distributions							(543)	(213)	(185)
Reclassification of Noncontrolling Interest - partially owned properties							8,514
Buyout of Noncontrolling Interest - partially owned properties							611
Change in fair value of interest rate cap agreements							13,708	0	0
Net (loss) income							31,424	12,741	(4,418)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, ending balance							13,708
General Partner
Increase (Decrease) in Partners' Capital [Roll Forward]
Trust Restricted share award grants, net	1,109					2,228
Total Partners’ Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Trust Restricted share award grants, net	1,109					2,228
Operating Partnership
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, beginning balance	1,076,461	$ 569,209	$ 1,076,461	$ 569,209	$ 1,076,461	569,209	1,076,461	569,209	240,837
Net proceeds from sale of Trust common shares and issuance of common units	321,238	301,772	764,205	318,041	764,292	318,170	766,841	545,117	350,385
Trust Restricted share award grants, net		846	2,329	1,879	3,203		4,434	2,908	2,060
Issuance of common shares in connection with the Ziegler shared service amendment payment									1,800
Purchase of OP Units		(205)	(2,129)	(253)	(2,999)	(253)	(3,671)	(1,088)	(7,546)
Conversion of OP Units		0	0	0	0	0	0	0	0
OP Units - distributions	(25,317)	(16,630)	(56,483)	(33,534)	(87,602)	(50,434)	(119,007)	(70,886)	(42,313)
Preferred distributions	(548)	(66)	(985)	(491)	(1,421)	(791)	(1,857)	(1,189)
Issuance of OP Units in connection with acquisition	2,869	7,314	2,869	10,733	2,869	10,973	23,848	10,973	28,589
Contributions		500		500	50	500	50	8,962
Distributions	(57)	(69)	(363)	(114)	(450)	(158)	(543)	(213)	(185)
Change in market value of Redeemable Limited Partners	(223)	56	(444)		(422)	92	(245)	(73)
Reclassification of Noncontrolling Interest - partially owned properties					(8,514)		(8,514)
Buyout of Noncontrolling Interest - partially owned properties					(611)		(611)
Change in fair value of interest rate cap agreements					652		13,708	0	0
Net (loss) income	5,424	(448)	12,608	2,849	22,902	6,832	31,424	12,741	(4,418)
Adjustments for Limited Partners ownership in Operating Partnership	0	0	0	0		0	0	0	0
Partners' capital, ending balance	1,380,956	862,279	1,798,068	868,819	1,768,410	856,368	1,782,318	1,076,461	569,209
Operating Partnership | Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners' Capital [Roll Forward]
Change in fair value of interest rate cap agreements					652		13,708
Partners' capital, ending balance					652
Operating Partnership | General Partner
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, beginning balance	1,021,132	534,730	1,021,132	534,730	1,021,132	534,730	1,021,132	534,730	204,904
Net proceeds from sale of Trust common shares and issuance of common units	321,238	301,772	764,205	318,041	764,292	318,170	766,841	545,117	350,385
Trust Restricted share award grants, net		846	2,329	1,879	3,203				2,060
Issuance of common shares in connection with the Ziegler shared service amendment payment									1,800
Conversion of OP Units	1,861	18	3,293	18	8,098	171	11,619	171	13,286
OP Units - distributions	(24,469)	(15,821)	(54,821)	(31,870)	(85,208)	(47,920)	(115,901)	(67,542)	(39,048)
Preferred distributions	(548)	(66)	(985)	(491)	(1,421)	(791)	(1,857)	(1,189)
Issuance of OP Units in connection with acquisition			(3,900)		(3,900)		17,079		0
Change in market value of Redeemable Limited Partners	(223)	56	(444)		(422)	92	(245)	(73)
Buyout of Noncontrolling Interest - partially owned properties					53		53
Net (loss) income	4,934	(456)	11,857	2,540	21,720	6,244	29,981	11,788	(4,037)
Adjustments for Limited Partners ownership in Operating Partnership	(1,783)	(2,445)	(4,545)	(1,815)	(6,680)	(1,642)	(8,393)	(4,778)	5,380
Partners' capital, ending balance	1,323,251	818,634	1,738,121	823,032	1,720,867	811,282	1,724,743	1,021,132	534,730
Operating Partnership | Limited Partner
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, beginning balance	45,451	33,727	45,451	33,727	45,451	33,727	45,451	33,727	35,310
Purchase of OP Units		(205)	(2,129)	(253)	(2,999)	(253)	(3,671)	(1,088)	(7,546)
Conversion of OP Units	(1,861)	(18)	(3,293)	(18)	(8,098)	(171)	(11,619)	(171)	(13,286)
OP Units - distributions	(848)	(809)	(1,662)	(1,664)	(2,394)	(2,514)	(3,106)	(3,344)	(3,265)
Issuance of OP Units in connection with acquisition	2,869	7,314	6,869	10,733	6,869	10,973	6,869	10,973	28,589
Net (loss) income	173	(24)	374	133	629	333	825	576	(695)
Adjustments for Limited Partners ownership in Operating Partnership	1,783	2,445	4,545	1,815	6,680	1,642	8,393	4,778	(5,380)
Partners' capital, ending balance	47,567	42,430	50,155	44,473	46,138	43,737	43,142	45,451	33,727
Operating Partnership | Total Partners’ Capital
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, beginning balance	1,066,583	568,457	1,066,583	568,457	1,066,583	568,457	1,066,583	568,457	240,214
Net proceeds from sale of Trust common shares and issuance of common units	321,238	301,772	764,205	318,041	764,292	318,170	766,841	545,117	350,385
Trust Restricted share award grants, net		846	2,329	1,879	3,203				2,060
Issuance of common shares in connection with the Ziegler shared service amendment payment									1,800
Purchase of OP Units		(205)	(2,129)	(253)	(2,999)	(253)	(3,671)	(1,088)	(7,546)
OP Units - distributions	(25,317)	(16,630)	(56,483)	(33,534)	(87,602)	(50,434)	(119,007)	(70,886)	(42,313)
Preferred distributions	(548)	(66)	(985)	(491)	(1,421)	(791)	(1,857)	(1,189)
Issuance of OP Units in connection with acquisition	2,869	7,314	2,969	10,733	2,969	10,973	23,948	10,973	28,589
Change in market value of Redeemable Limited Partners	(223)	56	(444)		(422)	92	(245)	(73)
Buyout of Noncontrolling Interest - partially owned properties					53		53
Change in fair value of interest rate cap agreements					652		13,708
Net (loss) income	5,107	(480)	12,231	2,673	22,349	6,577	30,806	12,364	(4,732)
Partners' capital, ending balance	1,370,818	861,064	1,788,276	867,505	1,767,657	855,019	1,781,593	1,066,583	568,457
Partially Owned Properties Noncontrolling Interest
Increase (Decrease) in Partners' Capital [Roll Forward]
Contributions							50	8,962
Distributions							(543)	(213)	(185)
Reclassification of Noncontrolling Interest - partially owned properties							(8,514)
Buyout of Noncontrolling Interest - partially owned properties							(664)
Net (loss) income							618	377	314
Partially Owned Properties Noncontrolling Interest | Operating Partnership
Increase (Decrease) in Partners' Capital [Roll Forward]
Partners' capital, beginning balance	9,878	752	9,878	752	9,878	752	9,878	752	623
Issuance of OP Units in connection with acquisition			(100)		(100)		(100)
Contributions		500		500	50	500	50	8,962
Distributions	(57)	(69)	(363)	(114)	(450)	(158)	(543)	(213)	(185)
Reclassification of Noncontrolling Interest - partially owned properties					(8,514)		(8,514)
Buyout of Noncontrolling Interest - partially owned properties					(664)		(664)
Net (loss) income	317	32	377	176	553	255	618	377	314
Partners' capital, ending balance	$ 10,138	$ 1,215	$ 9,792	$ 1,314	$ 753	$ 1,349	$ 725	$ 9,878	$ 752