Loans and Allowance for Loan Losses - Summary of Performance Status of Loan (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 1,024,200	$ 1,017,882
Percentage of Non-performing to Total	2.10%	3.43%
Recreation [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 609,999	$ 587,038
Percentage of Non-performing to Total	0.84%	0.99%
Home Improvement [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 193,275	$ 183,155
Percentage of Non-performing to Total	0.08%	0.07%
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 55,211	$ 64,083
Percentage of Non-performing to Total	7.72%	5.98%
Medallion [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 165,715	$ 183,606
Percentage of Non-performing to Total	7.23%	13.68%
Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 1,002,651	$ 983,005
Performing [Member] | Recreation [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	604,862	581,250
Performing [Member] | Home Improvement [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	193,117	183,018
Performing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	50,946	60,249
Performing [Member] | Medallion [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	153,726	158,488
Non - Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	21,549	34,877
Non - Performing [Member] | Recreation [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	5,137	5,788
Non - Performing [Member] | Home Improvement [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	158	137
Non - Performing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	4,265	3,834
Non - Performing [Member] | Medallion [Member]
Financing Receivable, Recorded Investment [Line Items]
Status of loans	$ 11,989	$ 25,118