Loans and Allowance for Loan Losses - Summary of the Company's Loan participations (Detail) - Loan Participations and Assignments - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 1,090,489	$ 1,024,709
Non-performing Loan Rate (%)	1.00%	0.65%
Impaired (%)	1.00%	0.65%
Gross Charge-offs	$ 0	$ 15
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 632,229	$ 598,873
Non-performing Loan Rate (%)	1.73%	1.11%
Impaired (%)	1.73%	1.11%
Gross Charge-offs	$ 0	$ 0
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 385,782	$ 306,202
Non-performing Loan Rate (%)	0.00%	0.00%
Impaired (%)	0.00%	0.00%
Gross Charge-offs	$ 0	$ 0
Commercial Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 72,374	$ 119,600
Non-performing Loan Rate (%)	0.00%	0.00%
Impaired (%)	0.00%	0.00%
Gross Charge-offs	$ 0	$ 0
Business banking
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 104	$ 34
Non-performing Loan Rate (%)	0.00%	0.00%
Impaired (%)	0.00%	0.00%
Gross Charge-offs	$ 0	$ 15

Non performing loan percentage.

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- Definition

Net credit losses are charge-offs and are based on total loans outstanding during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)(5)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Cost of the investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

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- Definition

Reflects the percentage derived from dividing impaired loans on which interest has ceased to be accrued by total loans.

+ References

No definition available.

+ Details

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