Debt - Summary of Senior Unsecured Credit Facility (Details) $ in Thousands, € in Millions, £ in Millions, ¥ in Billions	6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2021 JPY (¥)	Jun. 30, 2021 GBP (£)	Jun. 30, 2021 EUR (€)	Dec. 31, 2020 USD ($)
Senior Unsecured Credit Facility
Debt outstanding	$ 598,552				$ 405,433
Unamortized discount	33,386
Unsecured Term Loans:
Senior Unsecured Credit Facility
Debt outstanding	322,431				323,152
Unsecured Term Loans: | GBP
Senior Unsecured Credit Facility
Debt outstanding	207,750		£ 150.0		204,737
Unamortized discount	$ 1,000				1,200
Unsecured Term Loans: | GBP | GBP LIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	0.95%
Unsecured Term Loans: | EUR
Senior Unsecured Credit Facility
Debt outstanding	$ 114,681			€ 96.5	118,415
Unsecured Term Loans: | EUR | EURIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	0.95%
Unsecured Revolving Credit Facility:
Senior Unsecured Credit Facility
Debt outstanding	$ 276,121				82,281
Unsecured Revolving Credit Facility: | GBP
Senior Unsecured Credit Facility
Debt outstanding	$ 175,895		£ 127.0		0
Unsecured Revolving Credit Facility: | GBP | GBP LIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	0.85%
Unsecured Revolving Credit Facility: | EUR
Senior Unsecured Credit Facility
Debt outstanding	$ 78,435			€ 66.0	58,901
Unsecured Revolving Credit Facility: | EUR | EURIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	0.85%
Unsecured Revolving Credit Facility: | JPY
Senior Unsecured Credit Facility
Debt outstanding	$ 21,791	¥ 2.4			$ 23,380
Unsecured Revolving Credit Facility: | JPY | JPY LIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	0.85%