Operating expenses (Schedule of Depreciation and Amortization Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating expenses
Depreciation expense	$ 8,037	$ 7,168
Amortization expense	11,256	9,947
Total depreciation and amortization expenses	$ 19,293	$ 17,115