Income Taxes (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Difference between the Federal corporate tax rate and the effective tax rate
Income tax provision computed at US federal statutory rate	$ 11,859	$ 11,893	$ 14,777
Canadian rate differential	(1,398)	(1,050)	(1,287)
Change in uncertain tax positions, net of federal benefit	(3)	542	1,059
State and local income taxes, net of federal benefit	626	230	465
Other, net	(525)	(252)	101
Income tax expense (benefit)	$ 13,904	$ 11,363	$ 15,115
Income tax provision computed at US federal statutory rate, effective tax rate	35.00%	35.00%	35.00%
Canadian rate differential, effective tax rate	(4.10%)	(3.10%)	(3.00%)
Change in uncertain tax positions, net of federal income taxes, effective tax rate	0.00%	1.60%	2.50%
State and local income taxes, net of federal income taxes, effective tax rate	1.90%	0.60%	1.10%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 1,578
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	4.60%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 1,767
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Percent	5.20%
Other, net, effective tax rate	(1.60%)	(0.70%)	0.20%
Effective income tax rate	41.00%	33.40%	35.80%