Segment Information - Summarizes Revenue by Geographic Region (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues	$ 8,300	$ 9,833	$ 8,560	$ 9,307	$ 9,455	$ 9,817	$ 9,612	$ 9,091	$ 36,000	$ 37,975
United States
Segment Reporting Information [Line Items]
Revenues									21,476	22,686
Europe and Middle East
Segment Reporting Information [Line Items]
Revenues									4,720	4,843
Asia
Segment Reporting Information [Line Items]
Revenues									8,267	8,760
Other
Segment Reporting Information [Line Items]
Revenues									$ 1,537	$ 1,686