Segment Information - Summary of Sales to External Customers and Long-Lived Assets by Geographical Areas (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
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 89,867	$ 84,938	$ 81,646	$ 76,882	$ 82,848	$ 78,052	$ 77,511	$ 74,829	$ 333,333	$ 313,240	$ 294,129
Long-lived assets	53,168				39,051				53,168	39,051
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									142,679	139,079	130,791
Long-lived assets	38,729				25,901				38,729	25,901
Other American Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									6,404	6,032	4,841
Long-lived assets	116				120				116	120
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									149,083	145,111	135,632
Long-lived assets	38,845				26,021				38,845	26,021
Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									43,751	39,470	37,549
Long-lived assets	2,802				2,660				2,802	2,660
France [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									18,128	15,729	14,057
Long-lived assets	2,176				2,175				2,176	2,175
Other Europe, Middle East and Africa Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									40,050	34,909	35,933
Long-lived assets	4,534				4,317				4,534	4,317
Europe Middle East And Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									101,929	90,108	87,539
Long-lived assets	9,512				9,152				9,512	9,152
Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									33,686	33,198	26,795
Long-lived assets	2,237				879				2,237	879
Other Asia Pacific Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									48,635	44,823	44,163
Long-lived assets	2,574				2,999				2,574	2,999
Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									82,321	78,021	$ 70,958
Long-lived assets	$ 4,811				$ 3,878				$ 4,811	$ 3,878