Principal Business Activity and Significant Accounting Policies - Interest expense, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest expense, net
Interest expense	$ 14,495	$ 8,022	$ 1,563
Interest and other income	$ 400	$ 300	$ 100