XML 58 R44.htm IDEA: XBRL DOCUMENT v3.20.4
Summary of Significant Accounting Policies - Contracts assets and liabilities (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]      
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized $ 6,828,000 $ 1,240,000  
Impairment of Intangible Assets, Finite-lived $ 0 $ 0 $ 0