Finance Receivables, Credit Quality Information, and Allowance for Credit Losses - Summary of Financing Receivable Credit Quality Indicators (Detail) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	$ 221,206
2019		728,214
2018		121,430
2017		26,172
2016		4,015
Prior		1,248
Total Amortized Cost Basis		1,102,285	$ 1,133,404	$ 930,844
FICO Band 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	47,552
2019		129,127
2018		18,137
2017		4,802
2016		1,625
Prior		698
Total Amortized Cost Basis		201,941
FICO Band 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	21,615
2019		67,236
2018		9,019
2017		2,328
2016		648
Prior		220
Total Amortized Cost Basis		101,066
FICO Band 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	31,382
2019		109,710
2018		18,876
2017		4,411
2016		651
Prior		139
Total Amortized Cost Basis		165,169
FICO Band 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	35,063
2019		123,625
2018		20,438
2017		4,546
2016		376
Prior		129
Total Amortized Cost Basis		184,177
FICO Band 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	32,830
2019		115,086
2018		20,784
2017		4,288
2016		363
Prior		37
Total Amortized Cost Basis		173,388
FICO Band 6 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	52,764
2019		183,430
2018		34,176
2017		5,797
2016		352
Prior		25
Total Amortized Cost Basis		276,544
Small Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	114,256
2019		295,884
2018		28,851
2017		1,244
2016		42
Prior		9
Total Amortized Cost Basis		440,286	467,614	425,849
Small Loans [Member] | FICO Band 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	28,858
2019		71,925
2018		5,937
2017		413
2016		17
Prior		5
Total Amortized Cost Basis		107,155
Small Loans [Member] | FICO Band 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	12,978
2019		34,596
2018		3,050
2017		181
2016		9
Prior		2
Total Amortized Cost Basis		50,816
Small Loans [Member] | FICO Band 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	14,015
2019		36,106
2018		3,616
2017		179
2016		5
Prior		1
Total Amortized Cost Basis		53,922
Small Loans [Member] | FICO Band 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	15,166
2019		38,028
2018		3,524
2017		138
2016		4
Prior		1
Total Amortized Cost Basis		56,861
Small Loans [Member] | FICO Band 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	15,840
2019		40,468
2018		4,458
2017		133
2016		5
Total Amortized Cost Basis		60,904
Small Loans [Member] | FICO Band 6 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	27,399
2019		74,761
2018		8,266
2017		200
2016		2
Total Amortized Cost Basis		110,628
Large Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	104,438
2019		420,435
2018		86,600
2017		19,855
2016		1,102
Prior		159
Total Amortized Cost Basis		632,589	632,067	455,119
Large Loans [Member] | FICO Band 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	18,171
2019		55,211
2018		11,444
2017		2,678
2016		298
Prior		86
Total Amortized Cost Basis		87,888
Large Loans [Member] | FICO Band 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	8,265
2019		31,059
2018		5,239
2017		1,317
2016		130
Prior		12
Total Amortized Cost Basis		46,022
Large Loans [Member] | FICO Band 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	17,006
2019		72,020
2018		14,453
2017		3,305
2016		169
Prior		13
Total Amortized Cost Basis		106,966
Large Loans [Member] | FICO Band 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	19,336
2019		82,996
2018		15,553
2017		3,704
2016		158
Prior		32
Total Amortized Cost Basis		121,779
Large Loans [Member] | FICO Band 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	16,612
2019		72,574
2018		15,214
2017		3,732
2016		149
Prior		1
Total Amortized Cost Basis		108,282
Large Loans [Member] | FICO Band 6 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	25,048
2019		106,575
2018		24,697
2017		5,119
2016		198
Prior		15
Total Amortized Cost Basis		161,652
Automobile Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		3,638
2016		2,826
Prior		1,068
Total Amortized Cost Basis		7,532	9,640	20,556
Automobile Loans [Member] | FICO Band 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		1,535
2016		1,304
Prior		604
Total Amortized Cost Basis		3,443
Automobile Loans [Member] | FICO Band 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		661
2016		506
Prior		204
Total Amortized Cost Basis		1,371
Automobile Loans [Member] | FICO Band 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		741
2016		466
Prior		123
Total Amortized Cost Basis		1,330
Automobile Loans [Member] | FICO Band 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		391
2016		208
Prior		94
Total Amortized Cost Basis		693
Automobile Loans [Member] | FICO Band 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		127
2016		201
Prior		35
Total Amortized Cost Basis		363
Automobile Loans [Member] | FICO Band 6 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2017		183
2016		141
Prior		8
Total Amortized Cost Basis		332
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	2,512
2019		11,895
2018		5,979
2017		1,435
2016		45
Prior		12
Total Amortized Cost Basis		21,878	$ 24,083	$ 29,320
Retail Loans [Member] | FICO Band 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	523
2019		1,991
2018		756
2017		176
2016		6
Prior		3
Total Amortized Cost Basis		3,455
Retail Loans [Member] | FICO Band 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	372
2019		1,581
2018		730
2017		169
2016		3
Prior		2
Total Amortized Cost Basis		2,857
Retail Loans [Member] | FICO Band 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	361
2019		1,584
2018		807
2017		186
2016		11
Prior		2
Total Amortized Cost Basis		2,951
Retail Loans [Member] | FICO Band 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	561
2019		2,601
2018		1,361
2017		313
2016		6
Prior		2
Total Amortized Cost Basis		4,844
Retail Loans [Member] | FICO Band 5 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	378
2019		2,044
2018		1,112
2017		296
2016		8
Prior		1
Total Amortized Cost Basis		3,839
Retail Loans [Member] | FICO Band 6 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
2020	[1]	317
2019		2,094
2018		1,213
2017		295
2016		11
Prior		2
Total Amortized Cost Basis		$ 3,932

[1] Includes loans originated during the three month ended March 31, 2020.