Income Taxes - Narrative (Detail)	12 Months Ended						24 Months Ended
	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares		Dec. 31, 2016 USD ($) $ / shares		Dec. 31, 2014 operation_center	Dec. 31, 2018 USD ($)
Income Taxes [Line Items]
Income tax expense	$ 3,397,000	$ 36,146,000	[1]	$ 22,151,000	[1]
Effective tax rates	5.60%	42.50%
Transition tax	$ 176,000	$ 27,236,000					$ 27,412,000
Re-measured net deferred tax assets and liabilities, income tax expense		1,949,000
Measurement period increase to transition tax obligation	176,000						176,000
Transition tax obligation	27,412,000						27,412,000
Excess tax benefit on stock-based compensation	$ (7,227,000)	$ (9,797,000)		$ 0
Number of operation centers, income tax holiday expired | operation_center						3
Effective tax rate in Philippines post tax exemption	5.00%
Effect of diluted earnings per share, tax holiday (in dollars per share) | $ / shares	$ 0.16	$ 0.13		$ 0.12
Operating loss carryforward valuation allowance	$ 20,000	$ 20,000					20,000
Valuation allowance related to tax credit carry forward	79,000	88,000					79,000
Unrecognized tax benefits that would impact tax rate if recognized	804,000						804,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	0		$ 315,000
Accrued interest on unrecognized tax benefits	$ 0	68,000					0
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	$ 444,000	$ 1,554,000					$ 444,000

[1] Adjusted pursuant to adoption of ASU No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post-retirement Benefit Cost. Refer to Note 21 and Note 27 to the consolidated financial statements.