Debt - Summary of Senior Unsecured Credit Facility (Details) - Unsecured revolving credit facility $ in Thousands, € in Millions, ¥ in Billions	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 JPY (¥)	Jun. 30, 2019 EUR (€)	Dec. 31, 2018 USD ($)
Senior Unsecured Credit Facility
Debt	$ 111,227			$ 91,563
EUR
Senior Unsecured Credit Facility
Debt	$ 88,764		€ 78.0	69,273
EUR | EURIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	1.00%
JPY
Senior Unsecured Credit Facility
Debt	$ 22,463	¥ 2.4		$ 22,290
JPY | JPY LIBOR
Senior Unsecured Credit Facility
Variable interest rate (percentage)	1.00%