Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Narrative (Details)

v3.20.2
Fair Value Measurements - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2020
Dec. 31, 2019
Assets and liabilities measured at fair value on a recurring basis      
Marketable securities in deferred compensation plan $ 2,672 $ 2,672 $ 3,060
Fair value measurement on a recurring basis | Deferred compensation plan | Trustees and Management      
Assets and liabilities measured at fair value on a recurring basis      
Maximum percentage of participants' compensation which is deferrable (as a percent)   100.00%  
Marketable securities in deferred compensation plan 2,700 $ 2,700  
Fair Value, Nonrecurring | Baltimore, Maryland      
Assets and liabilities measured at fair value on a recurring basis      
Impairment losses $ 1,500