Variable Interest Entities and Noncontrolling Interests - Other variable interest entity disclosures (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 1,846,570	$ 1,848,679
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Total VIE Assets	3,112,109	3,425,833
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	3,702	(5,197)
Maximum Exposure to Loss - Off-Balance Sheet	38,554	42,084
Maximum Exposure to Loss	42,256	36,887
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2017-1 Ltd. (Oct-17)
Variable Interest Entity [Line Items]
Total VIE Assets	190,324	216,429
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	204	(442)
Maximum Exposure to Loss - Off-Balance Sheet	1,491	2,794
Maximum Exposure to Loss	1,695	2,352
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-1 Ltd. (Apr-18)
Variable Interest Entity [Line Items]
Total VIE Assets	299,909	328,482
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(132)	(1,574)
Maximum Exposure to Loss - Off-Balance Sheet	3,790	5,757
Maximum Exposure to Loss	3,658	4,183
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-2 Ltd. (Aug-18)
Variable Interest Entity [Line Items]
Total VIE Assets	380,986	437,009
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	83	(877)
Maximum Exposure to Loss - Off-Balance Sheet	2,787	2,524
Maximum Exposure to Loss	2,870	1,647
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2018-3 Ltd. (Oct-18)
Variable Interest Entity [Line Items]
Total VIE Assets	383,268	426,806
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	(116)	(1,113)
Maximum Exposure to Loss - Off-Balance Sheet	4,272	3,937
Maximum Exposure to Loss	4,156	2,824
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-1 Ltd. (Mar-19)
Variable Interest Entity [Line Items]
Total VIE Assets	228,940	257,358
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	396	(226)
Maximum Exposure to Loss - Off-Balance Sheet	3,072	3,027
Maximum Exposure to Loss	3,468	2,801
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-2 Ltd. (Apr-19)
Variable Interest Entity [Line Items]
Total VIE Assets	462,057	525,959
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	814	(78)
Maximum Exposure to Loss - Off-Balance Sheet	4,373	2,579
Maximum Exposure to Loss	5,187	2,501
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-3 Ltd. (Jul-19)
Variable Interest Entity [Line Items]
Total VIE Assets	603,465	656,523
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	1,033	(585)
Maximum Exposure to Loss - Off-Balance Sheet	8,449	9,273
Maximum Exposure to Loss	9,482	8,688
Variable Interest Entity, Not Primary Beneficiary | Bellemeade 2019-4 Ltd. (Oct-19)
Variable Interest Entity [Line Items]
Total VIE Assets	563,160	577,267
Maximum Exposure to Loss - On-Balance Sheet (Asset) Liability	1,420	(302)
Maximum Exposure to Loss - Off-Balance Sheet	10,320	12,193
Maximum Exposure to Loss	$ 11,740	$ 11,891