Loans Held for Investment - Loan Products Type and Characteristics (Details) $ in Thousands	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	139,194	140,345
Total Principal	$ 13,169,843	$ 12,432,581
30-89 Days Delinquent	1,458,079	1,171,771
90 Days Delinquent	$ 782,708	$ 795,504
Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	8,401	8,793
Total Principal	$ 912,993	$ 918,610
30-89 Days Delinquent	97,758	102,266
90 Days Delinquent	$ 62,545	$ 62,940
Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	130,793	131,552
Total Principal	$ 12,256,850	$ 11,513,971
30-89 Days Delinquent	1,360,321	1,069,505
90 Days Delinquent	$ 720,163	$ 732,564
$1 To $250 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	7,776	8,258
Total Principal	$ 655,914	$ 713,392
30-89 Days Delinquent	75,436	80,781
90 Days Delinquent	$ 44,117	$ 48,235
$1 To $250 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	123,580	126,085
Total Principal	$ 9,482,855	$ 9,566,517
30-89 Days Delinquent	1,021,054	894,574
90 Days Delinquent	$ 571,242	$ 591,283
$250 To $500 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	497	456
Total Principal	$ 163,972	$ 148,867
30-89 Days Delinquent	18,117	17,722
90 Days Delinquent	$ 10,950	$ 10,779
$250 To $500 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	6,259	4,942
Total Principal	$ 2,059,131	$ 1,595,673
30-89 Days Delinquent	275,574	160,015
90 Days Delinquent	$ 131,472	$ 128,876
$500 To $750 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	96	65
Total Principal	$ 56,661	$ 38,148
30-89 Days Delinquent	2,224	2,979
90 Days Delinquent	$ 2,747	$ 2,762
$500 To $750 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	712	406
Total Principal	$ 418,044	$ 238,292
30-89 Days Delinquent	46,972	12,239
90 Days Delinquent	$ 12,137	$ 10,600
$750 To $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	20	7
Total Principal	$ 16,947	$ 6,008
30-89 Days Delinquent	759	784
90 Days Delinquent	$ 862	$ 0
$750 To $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	137	88
Total Principal	$ 116,993	$ 75,289
30-89 Days Delinquent	6,224	2,677
90 Days Delinquent	$ 5,312	$ 1,805
Over $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	12	7
Total Principal	$ 19,499	$ 12,195
30-89 Days Delinquent	1,222	0
90 Days Delinquent	$ 3,869	$ 1,164
Over $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of Loans | loan	105	31
Total Principal	$ 179,827	$ 38,200
30-89 Days Delinquent	10,497	0
90 Days Delinquent	$ 0	$ 0
Maximum | $1 To $250 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	19.24%	19.49%
Maximum | $1 To $250 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	24.00%	24.00%
Maximum | $250 To $500 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	13.13%	12.75%
Maximum | $250 To $500 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	11.69%	12.52%
Maximum | $500 To $750 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	9.38%	10.00%
Maximum | $500 To $750 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	10.69%	10.69%
Maximum | $750 To $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	8.13%	5.13%
Maximum | $750 To $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	8.00%	7.98%
Maximum | Over $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	6.63%	5.00%
Maximum | Over $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	9.50%	6.38%
Minimum | $1 To $250 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	1.00%	1.00%
Minimum | $1 To $250 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	0.00%	0.00%
Minimum | $250 To $500 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	2.00%
Minimum | $250 To $500 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	0.00%	0.00%
Minimum | $500 To $750 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	2.00%
Minimum | $500 To $750 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	2.00%
Minimum | $750 To $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	1.97%	4.13%
Minimum | $750 To $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	2.00%
Minimum | Over $1,000 | Adjustable Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	4.00%
Minimum | Over $1,000 | Fixed Rate Loans
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Interest rate (as a percent)	2.00%	3.00%