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Fair Value Measurements - Changes in Level 3 inputs (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]        
Fair value at January 1, $ 16,169 $ 15,852 $ 15,852 $ 27,756
Interest expense accrued 37 150 150 364
Principal and interest expense paid     0 (13,328)
Increase in fair value (2,321) 167 167 1,060
Fair value at December 31, $ 13,885 $ 16,169 $ 16,169 $ 15,852