Segment Information - Schedule of Financial Information of Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information [Line Items]
Investment in unconsolidated real estate ventures	$ 85,912		$ 85,912		$ 103,007
Total assets	6,742,056		6,742,056		6,071,407
Total revenues	257,183	$ 197,497	730,859	$ 556,511
Operating expenses, including depreciation and amortization	134,459	100,193	404,205	302,164
Income (loss) from operations	122,724	97,304	326,654	254,347
Gain on real estate transactions and earnout from prior acquisition	0	1,101	9,814	1,501
Interest expense	(33,494)	(20,811)	(97,655)	(65,053)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(1,243)	(805)	(3,716)	(2,198)
Interest income	1,358	356	4,697	1,640
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213	3,638	3,638
Equity in earnings of unconsolidated real estate ventures	3,625	3,403	9,813	9,054
Equity in earnings of unconsolidated real estate ventures - gain on sale of real estate assets and purchase of partners' interests	37,509	0	64,432	2,857
Income tax (expense) benefit	(4,466)	(3,561)	(11,004)	(7,994)
Net income (loss)	127,226	78,200	306,673	197,792
Depreciation and amortization expense	46,555	30,711	133,402	92,691
Acquisition of real estate assets			(763,246)	(263,404)
Development and redevelopment of real estate assets			(18,492)	(15,137)
Rental Operations [Member]
Segment Reporting Information [Line Items]
Investment in unconsolidated real estate ventures	85,912		85,912		103,007
Total assets	6,427,600		6,427,600		5,674,030
Total revenues	224,451	170,548	635,730	480,466
Operating expenses, including depreciation and amortization	106,531	77,436	312,390	230,271
Income (loss) from operations	117,920	93,112	323,340	250,195
Interest expense	(32,619)	(20,034)	(95,125)	(63,894)
Equity in earnings of unconsolidated real estate ventures	3,625	3,403	9,813	9,054
Income tax (expense) benefit	(550)	(325)	(1,840)	(1,404)
Net income (loss)	88,376	76,156	236,188	193,951
Depreciation and amortization expense	44,189	28,558	126,506	85,940
Tenant Reinsurance [Member]
Segment Reporting Information [Line Items]
Total assets	35,021		35,021		37,696
Total revenues	22,727	18,226	64,936	52,076
Operating expenses, including depreciation and amortization	4,093	3,608	12,345	9,819
Income (loss) from operations	18,634	14,618	52,591	42,257
Interest income	4	3	10	11
Income tax (expense) benefit	(3,504)	(2,624)	(9,352)	(6,927)
Net income (loss)	15,134	11,997	43,249	35,341
Property Management, Acquisition and Development [Member]
Segment Reporting Information [Line Items]
Total assets	279,435		279,435		$ 359,681
Total revenues	10,005	8,723	30,193	23,969
Operating expenses, including depreciation and amortization	23,835	19,149	79,470	62,074
Income (loss) from operations	(13,830)	(10,426)	(49,277)	(38,105)
Gain on real estate transactions and earnout from prior acquisition	0	1,101	9,814	1,501
Interest expense	(875)	(777)	(2,530)	(1,159)
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes	(1,243)	(805)	(3,716)	(2,198)
Interest income	1,354	353	4,687	1,629
Interest income on note receivable from Preferred Operating Partnership unit holder	1,213	1,213	3,638	3,638
Equity in earnings of unconsolidated real estate ventures - gain on sale of real estate assets and purchase of partners' interests	37,509	0	64,432	2,857
Income tax (expense) benefit	(412)	(612)	188	337
Net income (loss)	23,716	(9,953)	27,236	(31,500)
Depreciation and amortization expense	2,366	2,153	6,896	6,751
Acquisition of real estate assets			(763,246)	(263,404)
Development and redevelopment of real estate assets			$ (18,492)	$ (15,137)