Quarterly report pursuant to Section 13 or 15(d)

Selected Balance Sheet Data - Additional Information (Detail)

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Selected Balance Sheet Data - Additional Information (Detail)
 3 Months Ended
Jan. 01, 2018
Jan. 01, 2017
Jan. 01, 2014
Mar. 31, 2018
USD ($)
Installments
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Mar. 31, 2013
USD ($)
Schedule Of Accrued Expenses [Line Items]              
SARs frozen liability amount       $ 18,706,000   $ 20,217,000  
Interest expense       $ 360,000 $ 382,000    
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 interest accrual commencement date       Jan. 01, 2014      
Interest expense       $ 225,000 $ 233,000    
Treasury note term     10 years        
Base spread on SARs liability variable rate     2.00%        
SARs liability interest accrual rates 4.409% 4.446%          
SARs liability number of annual installments | Installments       10      
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       $ 1,500,000      
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       $ 193,000      
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%