Variable Interest Entities and Noncontrolling Interests - Other variable interest entity disclosures (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Total VIE Assets	$ 41,199,648	$ 37,885,361
Maximum Exposure to Loss	1,906,196	1,848,679
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Total VIE Assets	3,035,349	3,425,833
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(4,708)	(5,197)
Maximum Exposure to Loss - Off-Balance Sheet	78,322	42,084
Maximum Exposure to Loss	73,614	36,887
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2017-1 Ltd. (Oct-17)
Variable Interest Entity [Line Items]
Total VIE Assets	145,573	216,429
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(295)	(442)
Maximum Exposure to Loss - Off-Balance Sheet	2,469	2,794
Maximum Exposure to Loss	2,174	2,352
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-1 Ltd. (Apr-18)
Variable Interest Entity [Line Items]
Total VIE Assets	250,095	328,482
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(1,244)	(1,574)
Maximum Exposure to Loss - Off-Balance Sheet	5,597	5,757
Maximum Exposure to Loss	4,353	4,183
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-2 Ltd. (Aug-18)
Variable Interest Entity [Line Items]
Total VIE Assets	272,685	437,009
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(1,206)	(877)
Maximum Exposure to Loss - Off-Balance Sheet	4,210	2,524
Maximum Exposure to Loss	3,004	1,647
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-3 Ltd. (Oct-18)
Variable Interest Entity [Line Items]
Total VIE Assets	302,563	426,806
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(1,883)	(1,113)
Maximum Exposure to Loss - Off-Balance Sheet	8,387	3,937
Maximum Exposure to Loss	6,504	2,824
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-1 Ltd. (Mar-19)
Variable Interest Entity [Line Items]
Total VIE Assets	219,256	257,358
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(83)	(226)
Maximum Exposure to Loss - Off-Balance Sheet	10,251	3,027
Maximum Exposure to Loss	10,168	2,801
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-2 Ltd. (Apr-19)
Variable Interest Entity [Line Items]
Total VIE Assets	398,316	525,959
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	54	(78)
Maximum Exposure to Loss - Off-Balance Sheet	13,088	2,579
Maximum Exposure to Loss	13,142	2,501
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-3 Ltd. (Jul-19)
Variable Interest Entity [Line Items]
Total VIE Assets	528,084	656,523
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(248)	(585)
Maximum Exposure to Loss - Off-Balance Sheet	10,649	9,273
Maximum Exposure to Loss	10,401	8,688
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-4 Ltd. (Oct-19)
Variable Interest Entity [Line Items]
Total VIE Assets	468,737	577,267
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	257	(302)
Maximum Exposure to Loss - Off-Balance Sheet	14,687	12,193
Maximum Exposure to Loss	14,944	$ 11,891
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2020-1 Ltd. (Jun-20)
Variable Interest Entity [Line Items]
Total VIE Assets	450,040
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(60)
Maximum Exposure to Loss - Off-Balance Sheet	8,984
Maximum Exposure to Loss	8,924
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2020-1 Ltd. (Jun-20) | Funded by directly provided capacity
Variable Interest Entity [Line Items]
Initial Coverage, Amount	$ 78,500