Geographic Information for Long-Lived Assets and Revenues in United States and other Countries (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Revenues	$ 49,570	$ 53,819	$ 57,989	$ 49,367	$ 60,341	$ 50,173	$ 43,572	$ 34,670	$ 210,745	$ 188,756
Reportable Geographical Components [Member]
Long-lived assets:
Long-lived assets	278,813				333,147				278,813	333,147
Revenues:
Revenues									210,745	188,756
Reportable Geographical Components [Member] | UNITED STATES
Long-lived assets:
Long-lived assets	272,903				326,665				272,903	326,665
Revenues:
Revenues									171,167	149,041
Reportable Geographical Components [Member] | International
Long-lived assets:
Long-lived assets	$ 5,910				$ 6,482				5,910	6,482
Reportable Geographical Components [Member] | CANADA
Revenues:
Revenues									6,086	7,439
Reportable Geographical Components [Member] | Other International
Revenues:
Revenues									$ 33,492	$ 32,276