Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Share Repurchase Program (Details)

v3.20.4
Summary of Significant Accounting Policies - Share Repurchase Program (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Aug. 31, 2019
Feb. 28, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Treasury stock, value $ 6,000 $ 144,000 $ 1,839,000      
Treasury Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Treasury stock, shares acquired (in shares) 455 10,300 217,774      
Treasury stock, value $ 6,000 $ 144,000 $ 1,839,000      
Class A Common Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock repurchase program, authorized amount (up to)       $ 17,553,000 $ 15,000,000 $ 10,000,000