Geographic Information - Schedule of Geographic Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenue	$ 24,957	$ 27,361	$ 30,305	$ 29,130	$ 29,774	$ 30,826	$ 34,024	$ 31,898	$ 111,753	$ 126,522	$ 116,704
UNITED STATES
Segment Reporting Information [Line Items]
Total revenue									98,736	108,200	100,730
CANADA
Segment Reporting Information [Line Items]
Total revenue									9,522	12,288	11,377
Non-US [Member]
Segment Reporting Information [Line Items]
Total revenue									$ 3,494	$ 6,034	$ 4,598