Principal Business Activity and Significant Accounting Policies - Receivables and Credit Policy (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Receivables and Credit Policy
Accounts receivable, gross	$ 99,118	$ 45,295
Less: Allowance for doubtful accounts	(330)	(216)
Non-current portion of receivables		72
Total accounts receivable, net	98,788	45,007
Trade receivables
Receivables and Credit Policy
Accounts receivable, gross	95,444	43,531
Other receivables
Receivables and Credit Policy
Accounts receivable, gross	$ 3,674	$ 1,764