Financial Derivatives and Hedging Activities - Outstanding Derivatives Used to Hedge Foreign Exchange Risks (Detail)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 PHP	Dec. 31, 2017 CAD	Dec. 31, 2017 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 PHP	Dec. 31, 2016 CAD	Dec. 31, 2016 GBP (£)
Cash Flow Hedges [Member] | Philippine Peso / British Pound [Member | Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | PHP			PHP 19,047,000
Cash Flow Hedges [Member] | Euro / British Pound [Member] | Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount		€ 13,586,000					€ 10,373,000
Cash Flow Hedges [Member] | Euro / U.S. Dollar [Member] | Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount		1,048,000
Cash Flow Hedges [Member] | Euro / U.S. Dollar [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | $	$ 60,519,000					$ 43,951,000
Cash Flow Hedges [Member] | Euro / Philippine Peso [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | PHP			890,096,000					PHP 699,279,000
Cash Flow Hedges [Member] | U.S Dollar / Euro [Member] | Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | $	946,000
Cash Flow Hedges [Member] | U.S Dollar / Euro [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount		4,253,000					15,379,000
Cash Flow Hedges [Member] | British Pound / Philippine Peso [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | PHP			PHP 797,496,000					PHP 557,025,000
Cash Flow Hedges [Member] | U.S. Dollar / Canadian Dollar [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | CAD				CAD 32,265,000					CAD 35,290,000
Cash Flow Hedges [Member] | British Pound / Euro [Member] | Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount		335,000
Foreign Currency Hedges [Member] | Euro / U.S. Dollar [Member] | Not Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | $	4,500,000					3,500,000
Foreign Currency Hedges [Member] | British Pound / Euro [Member] | Not Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | £					£ 1,000,000					£ 2,500,000
Foreign Currency Hedges [Member] | British Pound / Euro [Member] | Not Designated as Hedging [Member] | Buy Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount		€ 13,000,000					€ 18,500,000
Foreign Currency Hedges [Member] | U.S. Dollar / British Pound [Member] | Not Designated as Hedging [Member] | Sell Notional [Member]
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative notional amount | $	$ 17,500,000					$ 10,500,000