Loans and Allowance for Loan Losses - Summary of Nonperforming Loan Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment, With related allowance	$ 27,078	$ 48,702	$ 48,702	$ 27,078	$ 34,877
Unpaid principal balance, With related allowance	27,733	50,094	50,094	27,733	36,091
Related allowance, With related allowance	3,420	10,368	10,368	3,420	22,242
Average investment recorded, With related allowance	29,964	67,784	65,370	25,272
Interest income recognized, With related allowance	217	125	434	728
Recreation [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment, With related allowance	6,708	5,075	5,075	6,708	5,788
Unpaid principal balance, With related allowance	6,708	5,075	5,075	6,708	5,788
Related allowance, With related allowance	256	180	180	256	204
Average investment recorded, With related allowance	6,687	5,494	4,496	6,921
Interest income recognized, With related allowance	152	106	231	366
Home Improvement [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment, With related allowance	239	167	167	239	137
Unpaid principal balance, With related allowance	239	167	167	239	137
Related allowance, With related allowance	4	3	3	4	3
Average investment recorded, With related allowance	243	178	119	245
Interest income recognized, With related allowance	2			2
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment, With related allowance	12,031	5,403	5,403	12,031	3,834
Unpaid principal balance, With related allowance	12,126	5,814	5,814	12,126	3,929
Related allowance, With related allowance		100	100
Average investment recorded, With related allowance	9,616	7,047	5,838	6,827
Interest income recognized, With related allowance	36	(82)	(12)	321
Medallion [Member]
Financing Receivable, Recorded Investment [Line Items]
Recorded Investment, With related allowance	8,100	38,057	38,057	8,100	25,118
Unpaid principal balance, With related allowance	8,660	39,038	39,038	8,660	26,237
Related allowance, With related allowance	3,160	10,085	10,085	3,160	$ 22,035
Average investment recorded, With related allowance	13,418	55,065	54,917	11,279
Interest income recognized, With related allowance	$ 27	$ 101	$ 215	$ 39