Secured Borrowings (Details) $ in Thousands	1 Months Ended			3 Months Ended
	Mar. 31, 2020 USD ($) Option	Feb. 29, 2020 USD ($)	Jan. 31, 2020	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)
Secured Financing Agreements
Carrying Value	$ 9,689,683			$ 9,689,683		$ 8,906,048
Loss on extinguishment of debt				(170)	$ (3,298)
Purchased by investors	928,683			928,683		928,060
Payment of debt				1,923,754	$ 1,778,819
Revolving credit facility
Secured Financing Agreements
Maximum borrowing capacity	120,000			$ 120,000
Revolving credit facility | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				3.00%
Revolving Credit Agreement
Secured Financing Agreements
Maximum Facility Size	300,000			$ 300,000
Maximum facility size subject to certain conditions	$ 650,000			$ 650,000
Infrastructure Acquisition Facility
Secured Financing Agreements
Pricing margin (as a percent)				1.75%
Increase in spread in a subsequent period				0.25%
Property Mortgages - Fixed rate
Secured Financing Agreements
Maturity period				9 years 6 months
FHLB
Secured Financing Agreements
Pricing margin (as a percent)				1.99%
Interest rate (as a percent)	0.29%			0.29%
Carrying Value	$ 481,500			$ 481,500
Collateralized Loan Obligation
Secured Financing Agreements
Principal Amount							$ 86,600
Principal amount of notes							1,100,000
Purchased by investors							936,400
Liquidation preference							$ 77,000
Additional Contribution to CLO				82,500
Term loan facility
Secured Financing Agreements
Maximum borrowing capacity	398,000			$ 398,000
Term loan facility | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.50%
Commercial Loans
Secured Financing Agreements
Maximum Facility Size	8,900,000			$ 8,900,000
Carrying Value	$ 864,800			$ 864,800
Commercial Loans | LIBOR | Weighted-average
Secured Financing Agreements
Interest rate (as a percent)	1.92%			1.92%
Infrastructure Loans
Secured Financing Agreements
Extension term		1 year
CMBS/RMBS
Secured Financing Agreements
Interest rate (as a percent)	3.49%			3.49%
Maximum Facility Size	$ 0			$ 0
Carrying Value	184,500			184,500
Amount outstanding on a repurchase facility not subject to margin calls	184,500			184,500
Amount outstanding on repurchase facility	$ 42,900			$ 42,900
Pro rata share owned by a non-controlling partner in a consolidated joint venture	49.00%			49.00%
Amount of cash margin with lender pursuant to terms of related repurchase facility	$ 38,200			$ 38,200
CMBS/RMBS | LIBOR | Weighted-average
Secured Financing Agreements
Interest rate (as a percent)	1.66%			1.66%
CMBS/RMBS | Certain Facilities
Secured Financing Agreements
Carrying Value	$ 320,700			$ 320,700
Rolling maturity period				11 months
Maturity period				12 months
Primary beneficiary
Secured Financing Agreements
Equity Method Investment, Ownership Percentage			51.00%
Secured financing agreements
Secured Financing Agreements
Pledged Asset Carrying Value	12,431,687			$ 12,431,687
Maximum Facility Size	18,384,610			18,384,610
Principal Amount	9,778,305			9,778,305		9,000,125
Unamortized net discount	(8,089)			(8,089)		(8,347)
Unamortized deferred financing costs	(80,533)			(80,533)		(85,730)
Carrying Value	9,689,683			9,689,683		8,906,048
Increase in available borrowings	250,000
Secured financing agreements | Revolving credit facility
Secured Financing Agreements
Equity interests in certain subsidiaries used to secure facilities				3,100,000
Secured financing agreements | Other Secured Financing
Secured Financing Agreements
Pledged Asset Carrying Value	5,053,388			5,053,388
Maximum Facility Size	7,156,177			7,156,177
Principal Amount	4,554,180			4,554,180		4,390,668
Secured financing agreements | Revolving Credit Agreement
Secured Financing Agreements
Pledged Asset Carrying Value	273,429			273,429
Maximum Facility Size	650,000			650,000
Principal Amount	196,719			$ 196,719		198,955
Secured financing agreements | Revolving Credit Agreement | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.25%
Secured financing agreements | Commercial Financing Facility
Secured Financing Agreements
Pledged Asset Carrying Value	91,298			$ 91,298
Maximum Facility Size	73,763			73,763
Principal Amount	$ 73,763			$ 73,763
Maturity period	2 years
Number of extension options | Option	3
Extended term / option	1 year
Secured financing agreements | Commercial Financing Facility | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				1.75%
Secured financing agreements | Commercial Financing Facility | GBP LIBOR
Secured Financing Agreements
Pricing margin (as a percent)	1.75%
Secured financing agreements | Infrastructure Acquisition Facility
Secured Financing Agreements
Pledged Asset Carrying Value	$ 731,095			$ 731,095
Maximum Facility Size	740,382			740,382
Principal Amount	586,250			586,250		603,642
Secured financing agreements | Infrastructure Financing Facilities
Secured Financing Agreements
Pledged Asset Carrying Value	542,597			542,597
Maximum Facility Size	1,250,000			1,250,000
Principal Amount	448,848			448,848		428,206
Maximum borrowing capacity	750,000			$ 750,000
Secured financing agreements | Infrastructure Financing Facilities | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.12%
Secured financing agreements | Property Mortgages - Fixed rate
Secured Financing Agreements
Pricing margin (as a percent)				3.94%
Pledged Asset Carrying Value	1,488,698			$ 1,488,698
Maximum Facility Size	1,195,722			1,195,722
Principal Amount	1,195,722			1,195,722		1,196,492
Secured financing agreements | Property Mortgages - Variable rate
Secured Financing Agreements
Pledged Asset Carrying Value	777,925			777,925
Maximum Facility Size	728,310			728,310
Principal Amount	707,009			$ 707,009		696,503
Secured financing agreements | Property Mortgages - Variable rate | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.47%
Secured financing agreements | Term Loan and Revolver
Secured Financing Agreements
Maximum Facility Size	518,000			$ 518,000
Principal Amount	518,000			518,000		399,000
Secured financing agreements | FHLB
Secured Financing Agreements
Pledged Asset Carrying Value	1,148,346			1,148,346
Maximum Facility Size	2,000,000			2,000,000
Principal Amount	827,869			827,869		867,870
Secured financing agreements | Collateralized Loan Obligation
Secured Financing Agreements
Maximum borrowing capacity	$ 2,000,000			2,000,000
Additional extension term	4 years
Secured financing agreements | Repurchase Agreements
Secured Financing Agreements
Pledged Asset Carrying Value	$ 7,378,299			7,378,299
Maximum Facility Size	11,228,433			11,228,433
Principal Amount	5,224,125			5,224,125		4,609,457
Secured financing agreements | Commercial Loans
Secured Financing Agreements
Pledged Asset Carrying Value	5,882,347			5,882,347
Maximum Facility Size	9,156,617			9,156,617
Principal Amount	4,245,330			4,245,330		3,640,620
Maximum borrowing capacity		$ 1,800,000
Increase in available borrowings		$ 200,000
Secured financing agreements | Residential Loans
Secured Financing Agreements
Pledged Asset Carrying Value	12,486			12,486
Maximum Facility Size	400,000			400,000
Principal Amount	10,359			$ 10,359		11,835
Secured financing agreements | Residential Loans | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.10%
Secured financing agreements | Infrastructure Loans
Secured Financing Agreements
Pledged Asset Carrying Value	196,639			$ 196,639
Maximum Facility Size	500,000			500,000
Principal Amount	162,306			$ 162,306		188,198
Secured financing agreements | Infrastructure Loans | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				1.75%
Secured financing agreements | Conduit Loans
Secured Financing Agreements
Pledged Asset Carrying Value	182,575			$ 182,575
Maximum Facility Size	350,000			350,000
Principal Amount	123,353			$ 123,353		86,575
Extension term		1 year
Extended term / option		1 year
Secured financing agreements | Conduit Loans | LIBOR
Secured Financing Agreements
Pricing margin (as a percent)				2.16%
Secured financing agreements | CMBS/RMBS
Secured Financing Agreements
Pledged Asset Carrying Value	1,104,252			$ 1,104,252
Maximum Facility Size	821,816			821,816
Principal Amount	682,777			682,777		$ 682,229
Maturity period			12 months
Secured financing agreements | CMBS/RMBS | One-month LIBOR | Minimum
Secured Financing Agreements
Pricing margin (as a percent)			1.35%
Secured financing agreements | CMBS/RMBS | One-month LIBOR | Maximum
Secured Financing Agreements
Pricing margin (as a percent)			1.85%
Repurchase Agreements | Collateralized Loan Obligation
Secured Financing Agreements
Maximum borrowing capacity	$ 500,000			$ 500,000