Annual report pursuant to Section 13 and 15(d)

Selected Balance Sheet Data - Additional Information (Detail)

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Selected Balance Sheet Data - Additional Information (Detail)
 12 Months Ended
Jan. 01, 2018
Jan. 01, 2017
Jan. 01, 2016
Jan. 01, 2014
Dec. 31, 2018
USD ($)
Installments
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Mar. 31, 2013
USD ($)
Schedule Of Accrued Expenses [Line Items]                
Servicing portfolio of commercial real estate loans, unpaid principal balance         $ 1,600,000,000 $ 0    
SARs frozen liability amount         19,299,000 20,217,000    
Interest expense         $ 1,400,000 1,496,000 $ 1,533,000  
Maximum payment deferral period for certain commissions payable         3 years      
SARs [Member]                
Schedule Of Accrued Expenses [Line Items]                
SARs frozen liability amount               $ 20,000,000
SARs liability frozen value date         Mar. 31, 2013      
SARs liability number of annual installments | Installments         10      
SARs liability interest accrual commencement date         Jan. 01, 2014      
SARs liability interest accrual rates 4.409% 4.446% 4.273%          
Interest expense         $ 891,000 931,000 $ 914,000  
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         $ 1,700,000 1,400,000    
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 have been classified as current.      
Payments made during the period         $ 1,300,000 $ 607,000    
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%