Components of Income Tax Provision (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components Of Income Tax Expense Benefit [Line Items]
Current income tax provision (benefit)	$ 16,387	$ 12,285	$ 12,086
Deferred income tax provision (benefit)	(2,560)	(1,766)	(1,692)
Income Tax Provision (benefit)	13,827	10,519	10,394
CANADA
Components Of Income Tax Expense Benefit [Line Items]
Current income tax provision (benefit)	146	43	96
Deferred income tax provision (benefit)		0	0
UNITED STATES
Components Of Income Tax Expense Benefit [Line Items]
Current income tax provision (benefit)	9,434	9,678	8,136
Deferred income tax provision (benefit)	2,396	(2,378)	(3,239)
Other Countries
Components Of Income Tax Expense Benefit [Line Items]
Current income tax provision (benefit)	6,807	2,564	3,854
Deferred income tax provision (benefit)	$ (4,956)	$ 612	$ 1,547