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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Amount of decrease reasonably possible in the next twelve months for the unrecognized tax benefit.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of gain (loss) on sale or disposal of intangible assets.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount recognized for uncertainty in income taxes classified as noncurrent.

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Tax year that remains open to examination under enacted tax laws, in CCYY format.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended		12 Months Ended
	May 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018
Income Taxes
Unrecognized tax benefits		$ 3,800			$ 3,800
Unrecognized tax benefits would impact the effective tax rate		3,200			3,200
Unrecognized tax benefits expected to decrease in the next 12 months due to expiration of applicable statute of limitation		1,200			1,200
Interest accrued		700			$ 700
Effective tax rate from operations					22.40%	(3.80%)
Provision for (benefit from) income taxes		(291)		$ (1,240)	$ 6,419	$ (699)
Effective U.S corporate tax rate					21.00%		35.00%
Provision for transition tax								$ 37,200
Transition tax paid								8,300
Transition tax		28,900			$ 28,900
Transition Tax over an eight-year period beginning					2018
Retained earnings		571,322			$ 571,322			549,134
Undistributed foreign earnings		197,400			197,400
Other Long-term Liabilities
Income Taxes
Transition tax		28,000			28,000
Accounts Payable, Accrued Expenses and Operating Lease Liabilities
Income Taxes
Transition tax		900			900
Voice.com Domain Name
Income Taxes
Provision for (benefit from) income taxes	$ 8,100		$ 8,100
Voice.com Domain Name \| Other Income, Net
Income Taxes
Net gain on sale of domain name	$ 29,800		$ 29,800
U.S
Income Taxes
Cash and cash equivalents and short-term investments		311,900			$ 311,900			173,600
U.S \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2015
Italy \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2016
Poland \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2014
Spain \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2015
United Kingdom \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2017
Germany \| Earliest Tax Year
Income Taxes
Tax years subject to examination					2016
Foreign
Income Taxes
Cash and cash equivalents and short-term investments		$ 266,400			$ 266,400			402,500
Retained earnings								$ 397,400
Offshore receipts in respect of intangible property legislation tax payments percentage					20.00%