Operating expenses (Schedule of Depreciation and Amortization Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses
Depreciation expense	$ 7,837	$ 8,037
Amortization expense	13,233	11,256
Total depreciation and amortization expenses	$ 21,070	$ 19,293