Receivables and allowance for expected credit losses (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Credit Loss [Abstract]
Receivables past due 90 days or more	$ 51,800	$ 46,700	$ 38,300
Accounts Receivable, Allowance for Credit Loss	$ 11,125	$ 8,497	$ 9,600