Debt - Additional Information (Detail) - USD ($)		6 Months Ended
	Sep. 15, 2015	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Revolving line of credit		$ 85,000,000	$ 93,000,000
Silicon Valley Bank [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
New credit agreement entering date	Sep. 15, 2015
Maximum increase in secured credit facility	$ 200,000,000
Interest rate on outstanding borrowings		Borrowings under the Credit Facility bear a variable rate not less than zero based upon, at the Company’s option, either LIBOR or the higher of (i) the prime rate as published in the Wall Street Journal, and (ii) 0.5% plus the overnight federal funds rate, plus in each case, an applicable margin. The applicable margin for LIBOR loans, based on the applicable leverage ratio, is 1.25%, 1.50% or 1.75% per annum, and the applicable margin for base rate loans, based on the applicable leverage ratio, is either 0.25%, 0.50% or 0.75% per annum. At March 31, 2018, our rate, inclusive of applicable margins, was 3.6% for LIBOR, and at December 31, 2017, our rate, inclusive of applicable margins, was 3.1% for LIBOR.
Secured revolving credit facility, expiration date		Sep. 15, 2020
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | LIBOR Rate [Member]
Debt Instrument [Line Items]
Variable interest rate		3.80%	3.10%
Credit facility basis spread on variable rate LIBOR		0.50%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | New Credit Agreement [Member]
Debt Instrument [Line Items]
Secured revolving credit facility term, years	5 years
Secured revolving credit facility, current borrowing capacity	$ 150,000,000
Revolving line of credit		$ 85,000,000	$ 93,000,000
Secured revolving credit facility, available borrowing capacity		$ 64,500,000	56,500,000
Applicable leverage ratio, lower end		3.00%
Applicable leverage ratio		1.25%
Leverage ratio		2.04%
Fixed charge ratio		3.12%
Percentage of equity interest in direct foreign subsidiaries pledged		65.00%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | New Credit Agreement [Member] | LIBOR Rate [Member]
Debt Instrument [Line Items]
Applicable leverage ratio, lower end		1.25%
Applicable leverage ratio		1.50%
Applicable leverage ratio, higher end		1.75%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | New Credit Agreement [Member] | Base Rate [Member]
Debt Instrument [Line Items]
Applicable leverage ratio, lower end		0.25%
Applicable leverage ratio		0.50%
Applicable leverage ratio, higher end		0.75%
Silicon Valley Bank [Member] | Stand-by letter of credit [Member] | New Credit Agreement [Member]
Debt Instrument [Line Items]
Secured revolving credit facility, current borrowing capacity		$ 500,000	$ 500,000