Income Taxes - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 operation_center
Income Taxes [Line Items]
Effective tax rates	42.50%	26.40%
Re-measured net deferred tax assets and liabilities, income tax expense	$ 1,949,000
Provisional transition tax obligation	27,236,000
Excess tax benefit	$ 9,797,000	$ 0	$ 0
Number of operation centers, income tax holiday expired | operation_center				2
Effective tax rate in Philippines post tax exemption	5.00%
Effect of diluted earnings per share, tax holiday (in dollars per share) | $ / shares	$ 0.13	$ 0.12	$ 0.09
Operating loss carryforward valuation allowance	$ 20,000	$ 351,000
Valuation allowance related to tax credit carry forward	88,000	103,000
Deferred income taxes provided for Company's share of undistributed net earnings of foreign operations		0
Undistributed net earnings of foreign operations	376,649,000
Unrecognized tax benefits	824,000	3,087,000
Recognized interest and penalties	0	315,000
Accrued interest on unrecognized tax benefits	$ 68,000	1,553,000
First Five Years
Income Taxes [Line Items]
Percentage of tax exemption on profit	100.00%
Five to Ten Years
Income Taxes [Line Items]
Percentage of tax exemption on profit	50.00%
Expiration 2032
Income Taxes [Line Items]
Operating loss carryforwards	$ 1,554,000	$ 4,052,000
Operating loss carry forwards expiration date	2032