Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Retirement Benefits (Details)

v3.20.4
Summary of Significant Accounting Policies - Retirement Benefits (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Summary of Significant Accounting Policies      
Pension contributions $ 2,070,000 $ 1,904,000 $ 1,847,000