Income Taxes - Reconciliation of Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Canadian Federal
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	$ 2,617	$ 1,693	$ 1,095
Gross increase — current period tax positions	1,651	924	588
Gross decrease — prior period tax positions	0	0	0
Gross increase — prior period tax positions	0	0	11
Expiration of statute of limitations	0	0	(1)
Unrecognized tax positions, end of year	4,268	2,617	1,693
Canadian Provincial
Reconciliation of the beginning and ending gross amounts of unrecognized tax positions
Unrecognized tax positions, beginning of year	8,010	7,556	7,333
Gross increase — current period tax positions	638	454	227
Gross decrease — prior period tax positions	0	0	(3)
Gross increase — prior period tax positions	0	0	0
Expiration of statute of limitations	0	0	(1)
Unrecognized tax positions, end of year	$ 8,648	$ 8,010	$ 7,556