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Fair Value Measurements - Quantitative Information Related to Significant Unobservable Inputs (Detail) - Fair Value Measurements, Recurring [Member] - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Privately Issued Mortgage-Backed Securities [Member] | Two Independent Pricing Quotes [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Recurring fair value measurements for certain Level 3 Assets and Liabilities $ 16 $ 16
Other Assets and Other Liabilities [Member] | Discounted Cash Flows [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Recurring fair value measurements for certain Level 3 Assets and Liabilities $ 43,234 $ 10,740
Other Assets and Other Liabilities [Member] | Discounted Cash Flows [Member] | Minimum [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Commitment expirations 0.00% 0.00%
Other Assets and Other Liabilities [Member] | Discounted Cash Flows [Member] | Maximum [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Commitment expirations 98.00% 99.00%
Other Assets and Other Liabilities [Member] | Discounted Cash Flows [Member] | Weighted Average [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]    
Commitment expirations 16.00% 13.00%