Quarterly report pursuant to Section 13 or 15(d)

Selected Balance Sheet Data - Additional Information (Detail)

v3.20.2
Selected Balance Sheet Data - Additional Information (Detail) - USD ($)
 3 Months Ended 6 Months Ended
Jan. 01, 2020
Jan. 01, 2019
Jan. 01, 2014
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Mar. 31, 2013
Schedule Of Accrued Expenses [Line Items]                  
SARs frozen liability amount       $ 16,316,000   $ 16,316,000   $ 18,122,000  
Interest expense       213,000 $ 340,000 $ 496,000 $ 689,000    
Maximum payment deferral period for certain commissions payable           3 years      
Mortgage servicing rights [Member]                  
Schedule Of Accrued Expenses [Line Items]                  
Servicing portfolio of commercial real estate loans, unpaid principal balance       1,700,000,000   $ 1,700,000,000   1,600,000,000  
Escrow Funds       2,700,000   $ 2,700,000   $ 2,600,000  
SARs [Member]                  
Schedule Of Accrued Expenses [Line Items]                  
SARs frozen liability amount                 $ 20,000,000.0
SARs liability frozen value date           Mar. 31, 2013      
SARs liability interest accrual commencement date           Jan. 01, 2014      
SARs liability interest accrual rates 3.92% 4.684%              
Interest expense       $ 177,000 $ 226,000 $ 355,000 452,000    
Treasury note term     10 years            
Base spread on SARs liability variable rate     2.00%            
Estimated payouts description           Estimated payouts within the next twelve months for participants that have separated from service have been classified as current.      
Payments made during the period           $ 2,100,000 1,700,000    
Deferred Compensation Liability [Member]                  
Schedule Of Accrued Expenses [Line Items]                  
Estimated payouts description           Estimated payouts within the next twelve months for participants that have separated from service or elected in service payout have been classified as current.      
Deferred Compensation Liability, Minimum Payout Period           2 years      
Deferred Compensation Liability, Maximum Payout Period           15 years      
Fair value of deferred compensation plan assets           110.00%      
Payments made during the period           $ 821,000 $ 786,000