General form of registration statement for all companies including face-amount certificate companies

Commitments and Contingencies - Additional Information (Detail)

v3.21.2
Commitments and Contingencies - Additional Information (Detail) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Commitments And Contingencies Disclosure [Line Items]            
Lessee, Operating Lease, Term of Contract         2026 years  
Operating Leases, Rent Expense         $ 2,500,000 $ 2,300,000
Operating lease rent expenses net $ 600,000 $ 700,000 $ 2,000,000.0 $ 2,000,000.0    
Lessee, operating lease, description         March 2021 to May 2025  
Standby Letters Of Credit And Bank Guarantee [Member]            
Commitments And Contingencies Disclosure [Line Items]            
Off balance sheet credit exposure $ 400,000   $ 400,000   $ 400,000  
TMobile US, Inc [Member]            
Commitments And Contingencies Disclosure [Line Items]            
Gain (Loss) on Extinguishment of Debt         2,300,000  
Standby Letters of Credit [Member]            
Commitments And Contingencies Disclosure [Line Items]            
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expense (Reversal)         400,000 $ 400,000
Hardware And Software Leases [Member] | Maximum [Member]            
Commitments And Contingencies Disclosure [Line Items]            
Operating Leases, Rent Expense         43,146  
Hardware And Software Leases [Member] | Minimum [Member]            
Commitments And Contingencies Disclosure [Line Items]            
Operating Leases, Rent Expense         $ 667