Shareholders' Equity, Noncontrolling Interests and Other Comprehensive Income - Noncontrolling Interest (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				$ 589,548					$ 589,548
Net income (loss)	$ 24,944	$ 13,285	$ 6,108	$ 19,971	$ 34,236	$ 326	$ 26,155	$ 73,875	64,308	$ 134,592	$ 149,970
Conversion of Common OP Units to Common Shares by limited partners of the Operating Partnership									0	0	0
Issuance of OP Units to acquire real estate										31,429
Acquisition of noncontrolling interests										(18,379)	(7,970)
Other comprehensive income - unrealized loss on valuation of swap agreements									634	(646)	(5,061)
Change in control of previously unconsolidated investment										(75,713)
Reclassification of realized interest on swap agreements									3,317	4,576	5,524
Noncontrolling interest contributions									85,206	295,108	35,489
Noncontrolling interest distributions									(32,805)	(80,769)	(74,950)
Employee Long-term Incentive Plan Unit Awards									11,155	13,694	8,644
Rebalancing adjustment									0	0
Balance	$ 648,440				$ 589,548				648,440	589,548
Payments to noncontrolling interests									$ 39,942	$ 105,994	$ 84,610
Distributions declared (in dollars per share)	$ 0.27	$ 0.26	$ 0.26	$ 0.26	$ 0.41	$ 0.25	$ 0.25	$ 0.25	$ 1.05	$ 1.16	$ 1.22
Preferred shares converted to common stock (in shares)	5,000								5,000
Limited partners' capital account, units issued and converted (in shares)	81,453				351,250				81,453	351,250
Fund II
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Additional ownership interest acquired								8.30%
Payments to noncontrolling interests								$ 18,400
Equity Interest Held By Operating Partnership								28.33%
LTIP Units
Increase (Decrease) in Stockholders' Equity [Roll Forward]
LTIP units outstanding (in shares)	2,274,147				1,997,099				2,274,147	1,997,099
Series A Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Limited partners' capital account, units issued and converted (in shares)	1,392								1,392
Restatement Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				$ (35,700)				$ (31,800)	$ (35,700)	$ (31,800)
Net income (loss)					$ (4,200)					(4,200)
Balance					$ (35,700)					$ (35,700)	$ (31,800)
Operating Partnership, as General Partner or Managing Member
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Series A Preferred OP Units (in shares)	3,328,873				3,308,875				3,328,873	3,308,875
Equity Interest Held By Operating Partnership									95.00%	95.00%
Operating Partnership, as General Partner or Managing Member | Series A Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Series A Preferred OP Units (in shares)	188				188				188	188
Operating Partnership, as General Partner or Managing Member | Series C Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Series A Preferred OP Units (in shares)	136,593				141,593				136,593	141,593
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				589,548				420,866	$ 589,548	$ 420,866
Distributions declared of $0.78 and $1.16 per Common OP Unit for Years Ended 2017 and 2016, respectively									(6,453)	(6,753)
Net income (loss)									2,838	61,816
Conversion of Common OP Units to Common Shares by limited partners of the Operating Partnership									(1,541)	(7,892)	(2,451)
Issuance of OP Units to acquire real estate										31,429
Acquisition of noncontrolling interests										(25,925)	(3,561)
Other comprehensive income - unrealized loss on valuation of swap agreements									(147)	(332)
Change in control of previously unconsolidated investment										(75,713)
Reclassification of realized interest on swap agreements									686	597
Noncontrolling interest contributions									85,206	295,108	35,489
Noncontrolling interest distributions									(32,805)	(80,769)	(74,950)
Employee Long-term Incentive Plan Unit Awards									10,457	12,768	6,723
Rebalancing adjustment									651	(35,652)
Balance	$ 648,440				$ 589,548				648,440	589,548	420,866
Noncontrolling Interests | Restatement Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	651								651
Noncontrolling Interests | Noncontrolling Interests in Partially-Owned Affiliates
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				494,126				324,526	494,126	324,526
Distributions declared of $0.78 and $1.16 per Common OP Unit for Years Ended 2017 and 2016, respectively									0	0
Net income (loss)									(1,321)	56,814
Conversion of Common OP Units to Common Shares by limited partners of the Operating Partnership									0	0
Issuance of OP Units to acquire real estate										0
Acquisition of noncontrolling interests										(25,925)
Other comprehensive income - unrealized loss on valuation of swap agreements									(232)	(289)
Change in control of previously unconsolidated investment										(75,713)
Reclassification of realized interest on swap agreements									545	374
Noncontrolling interest contributions									85,206	295,108
Noncontrolling interest distributions									(32,805)	(80,769)
Employee Long-term Incentive Plan Unit Awards									0	0
Rebalancing adjustment										0
Balance	545,519				494,126				545,519	494,126	324,526
Noncontrolling Interests | Noncontrolling Interests in Partially-Owned Affiliates | Restatement Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	0								0
Noncontrolling Interests | Operating Partnership, as General Partner or Managing Member
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance				$ 95,422				$ 96,340	95,422	96,340
Distributions declared of $0.78 and $1.16 per Common OP Unit for Years Ended 2017 and 2016, respectively									(6,453)	(6,753)
Net income (loss)									4,159	5,002
Conversion of Common OP Units to Common Shares by limited partners of the Operating Partnership									(1,541)	(7,892)
Issuance of OP Units to acquire real estate										31,429
Acquisition of noncontrolling interests										0
Other comprehensive income - unrealized loss on valuation of swap agreements									85	(43)
Change in control of previously unconsolidated investment										0
Reclassification of realized interest on swap agreements									141	223
Noncontrolling interest contributions									0	0
Noncontrolling interest distributions									0	0
Employee Long-term Incentive Plan Unit Awards									10,457	12,768
Rebalancing adjustment										(35,652)
Balance	102,921				$ 95,422				102,921	$ 95,422	$ 96,340
Noncontrolling Interests | Operating Partnership, as General Partner or Managing Member | Restatement Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 651								$ 651