Consolidated Statements of Income - USD ($) $ in Thousands													3 Months Ended								12 Months Ended
	Nov. 07, 2017	Sep. 01, 2017	Jun. 01, 2017	Mar. 01, 2017	Dec. 02, 2016	Sep. 01, 2016	Jun. 01, 2016	Apr. 01, 2016	Dec. 01, 2015	Sep. 01, 2015	Jun. 08, 2015	Mar. 12, 2015	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
Net interest income
Interest income													$ 73,352	$ 66,833	$ 65,970	$ 57,512	$ 60,721	$ 60,284	$ 55,766	$ 59,601	$ 263,667	$ 236,372	$ 241,539
Interest expense																					146,118	120,827	113,303
Net interest income																					117,549	115,545	128,236
Provision for loan losses																					0	300	600
Net interest income after provision for loan losses													31,795	29,348	30,309	26,097	28,517	29,599	27,214	29,915	117,549	115,245	127,636
Other income
Operating lease income																					89,492	77,277	80,465
Tenant recoveries																					7,179	5,958	9,907
Sale of loans, net																					54,046	26,009	71,066
Realized gain (loss) on securities																					17,209	7,724	24,007
Unrealized gain (loss) on Agency interest-only securities																					1,405	(56)	(1,249)
Realized gain on sale of real estate, net																					11,423	20,636	40,386
Fee and other income																					18,341	21,365	15,205
Net result from derivative transactions																					(12,641)	(1,409)	(38,937)
Earnings (loss) from investment in unconsolidated joint ventures																					89	426	371
Gain (loss) on extinguishment of debt																					(73)	5,382	0
Total other income																					186,470	163,312	201,221
Costs and expenses
Salaries and employee benefits																					70,463	64,270	61,612
Operating expenses																					21,421	20,552	25,103
Real estate operating expenses																					33,216	30,545	37,869
Fee expense																					4,996	3,703	4,521
Depreciation and amortization																					40,332	39,447	39,061
Total costs and expenses													52,804	39,244	40,120	38,260	45,335	40,615	37,405	35,162	170,428	158,517	168,166
Income (loss) before taxes													48,427	29,245	37,664	18,255	72,394	58,319	1,644	(12,317)	133,591	120,040	160,691
Income tax expense (benefit)													3,057	(576)	6,606	(1,375)	773	8,721	(2,301)	(873)	7,712	6,320	14,557
Net income (loss)													45,370	29,821	31,058	19,630					125,879	113,720	146,134
Net (income) loss attributable to noncontrolling interest in consolidated joint ventures													(92)	265	(77)	(322)	(298)	439	(235)	232	(226)	138	(1,568)
Net (income) loss attributable to noncontrolling interest in operating partnership													$ (9,172)	$ (6,499)	$ (8,868)	$ (5,838)	$ (29,467)	$ (22,429)	$ (908)	$ 5,673	$ (30,377)	$ (47,131)	$ (70,745)
Earnings per share:
Basic (in dollars per share)													$ 0.41	$ 0.28	$ 0.28	$ 0.18	$ 0.64	$ 0.44	$ 0.05	$ (0.09)	$ 1.16	$ 1.08	$ 1.43
Diluted (in dollars per share)													0.40	0.28	0.26	0.18	0.63	0.44	0.05	(0.09)	$ 1.13	$ 1.06	$ 1.42
Weighted average shares outstanding:
Basic (in shares)																					81,902,524	61,998,089	51,702,188
Diluted (in shares)																					109,704,880	107,638,788	51,870,808
Dividends per share of Class A common stock (in dollars per share)													$ 0.315	$ 0.3	$ 0.3	$ 0.3	$ 0.46	$ 0.275	$ 0.275	$ 0.275
Class A Common Stock
Costs and expenses
Net income (loss) attributable to Class A common shareholders													$ 36,106	$ 23,587	$ 22,113	$ 13,470	$ 41,856	$ 27,608	$ 2,802	$ (5,539)	$ 95,276	$ 66,727	$ 73,821
Earnings per share:
Basic (in dollars per share)																					$ 1.16	$ 1.08	$ 1.43
Diluted (in dollars per share)																					$ 1.13	$ 1.06	$ 1.42
Weighted average shares outstanding:
Basic (in shares)																					81,902,524	61,998,089	51,702,188
Diluted (in shares)																					109,704,880	107,638,788	51,870,808
Dividends per share of Class A common stock (in dollars per share)	$ 0.315	$ 0.3	$ 0.3	$ 0.3	$ 0.46	$ 0.275	$ 0.275	$ 0.275	$ 1.45	$ 0.275	$ 0.25	$ 0.25									$ 1.215	$ 1.285	$ 2.225