Business combinations - Schedule of Identifiable Intangible Assets Acquired (Details) - Sagicor $ in Thousands	Jun. 01, 2018 USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value, unfavorable ground lease liability	$ (2,349)
Weighted-Average Amortization Period, unfavorable ground lease liability	22 years
Total identifiable intangibles acquired	$ (449)
Management agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated Fair Value, intangible assets	$ 1,900
Weighted-Average Amortization Period, intangible assets	20 years