Total Revenues Gross Profit and Long Lived Assets Excluding Long Term Deferred Tax Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets
Total revenues	$ 122,152	$ 126,010	$ 365,721	$ 367,462
Gross profit	98,763	101,621	292,107	295,566
Long-lived assets	59,410		59,410		$ 63,269
Domestic
Revenues from External Customers and Long-Lived Assets
Total revenues	70,611	73,443	210,715	222,245
Gross profit	56,549	58,720	166,839	177,882
Long-lived assets	50,215		50,215		55,355
EMEA
Revenues from External Customers and Long-Lived Assets
Total revenues	37,628	40,081	113,834	107,833
Gross profit	30,779	32,779	91,540	87,008
Long-lived assets	5,825		5,825		5,626
Other Regions
Revenues from External Customers and Long-Lived Assets
Total revenues	13,913	12,486	41,172	37,384
Gross profit	11,435	$ 10,122	33,728	$ 30,676
Long-lived assets	$ 3,370		$ 3,370		$ 2,288