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Debt - UK Bilateral Revolving Credit Facility (Details) - Revolving Credit Facility - UK Bilateral Revolving Credit Facility
$ in Thousands
Sep. 24, 2018
USD ($)
Sep. 24, 2018
GBP (£)
Dec. 31, 2019
Dec. 31, 2018
Debt Instrument [Line Items]        
Maximum borrowing capacity   £ 140,000,000    
Optional additional commitments   125,000,000    
Proceeds from lines of credit $ 180,300 £ 138,250,000    
Debt instrument, basis spread on variable rate 2.25% 2.25%    
Effective interest rate (as a percent)     3.10% 3.10%