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Financial Derivatives and Hedging Activities - Outstanding Derivatives Used to Hedge Foreign Exchange Risks (Detail) | Sep. 30, 2017 USD ($) | Sep. 30, 2017 EUR (€) | Sep. 30, 2017 PHP | Sep. 30, 2017 CAD | Sep. 30, 2017 GBP (£) | Dec. 31, 2016 USD ($) | Dec. 31, 2016 EUR (€) | Dec. 31, 2016 PHP | Dec. 31, 2016 CAD | Dec. 31, 2016 GBP (£)
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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 | € |  | € 11,428,000 |  |  |  |  | € 10,373,000 |  |  |
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 |  |  | 857,103,000 |  |  |  |  | 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 | $ 1,471,000 |  |  |  |  |  |  |  |  |
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 | € |  | 7,799,000 |  |  |  |  | 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 644,076,000 |  |  |  |  | PHP 557,025,000 |  |
Cash Flow Hedges [Member] | Canadian Dollar / U.S. Dollar [Member] | Designated as Hedging [Member] | Sell Notional [Member] |  |  |  |  |  |  |  |  |  |
Derivative Instruments And Hedging Activities Disclosures [Line Items] |  |  |  |  |  |  |  |  |  |
Derivative notional amount | 20,000 |  |  |  |  |  |  |  |  |
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 | 54,135,000 |  |  |  |  | $ 43,951,000 |  |  |  |
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 32,760,000 |  |  |  |  | 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 | € |  | € 12,000,000 |  |  |  |  | € 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 |  |  |  |

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