Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 30,616	$ 32,582	$ 32,582
Charge-offs	(510)	(726)	(3,639)
Recoveries	892	1,808	3,363
Provision (benefit)	8,000	(1,600)	(1,690)
Ending balance	57,911	32,064	30,616
Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	18,913
Ending balance			18,913
Mortgage Loans on Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	14,301	15,620	15,620
Charge-offs	0	0	(748)
Recoveries	604	1,383	1,582
Provision (benefit)	5,475	(2,173)	(2,153)
Ending balance	34,903	14,830	14,301
Mortgage Loans on Real Estate \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	14,523
Ending balance			14,523
Mortgage Loans on Real Estate \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11,995	12,944	12,944
Charge-offs	0	0	(746)
Recoveries	194	1,381	1,528
Provision (benefit)	5,216	(1,995)	(1,731)
Ending balance	29,253	12,330	11,995
Mortgage Loans on Real Estate \| Commercial \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11,848
Ending balance			11,848
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	7,778	8,375	8,375
Charge-offs	(130)	(207)	(768)
Recoveries	142	257	1,256
Provision (benefit)	543	(84)	(1,085)
Ending balance	13,942	8,341	7,778
Consumer \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,609
Ending balance			5,609
Consumer \| Home equity lines of credit
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,572	6,042	6,042
Charge-offs	0	0	0
Recoveries	33	95	504
Provision (benefit)	369	(122)	(974)
Ending balance	10,523	6,015	5,572
Consumer \| Home equity lines of credit \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,549
Ending balance			4,549
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,149	6,090	6,090
Charge-offs	(380)	(519)	(2,123)
Recoveries	146	168	525
Provision (benefit)	1,708	339	657
Ending balance	4,471	6,078	5,149
Commercial \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(2,152)
Ending balance			(2,152)
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,388	2,497	2,497
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	274	318	891
Ending balance	4,595	2,815	3,388
Construction \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	933
Ending balance			933
Construction \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,758	2,033	2,033
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	269	234	725
Ending balance	3,771	2,267	2,758
Construction \| Commercial \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	744
Ending balance			744
Construction \| Residential
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	630	464	464
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	5	84	166
Ending balance	824	548	630
Construction \| Residential \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	189
Ending balance			189
Residential 1-4 family \| Mortgage Loans on Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,306	2,676	2,676
Charge-offs	0	0	(2)
Recoveries	410	2	54
Provision (benefit)	259	(178)	(422)
Ending balance	5,650	2,500	2,306
Residential 1-4 family \| Mortgage Loans on Real Estate \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,675
Ending balance			2,675
Home equity loans \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	611	1,540	1,540
Charge-offs	0	0	(3)
Recoveries	15	87	431
Provision (benefit)	(42)	(341)	(1,357)
Ending balance	673	1,286	611
Home equity loans \| Consumer \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	89
Ending balance			89
Other \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,595	793	793
Charge-offs	(130)	(207)	(765)
Recoveries	94	75	321
Provision (benefit)	216	379	1,246
Ending balance	2,746	$ 1,040	1,595
Other \| Consumer \| Impact of CECL Adoption
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 971
Ending balance			$ 971

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- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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