Derivative Financial Instruments - Summary of Outstanding Foreign Exchange Derivatives Designated as Net Investment Hedges of Foreign Currency Risk (Detail) - Sell [Member] - Designated as Hedging Instrument [Member] - Foreign Exchange Forward [Member] - Net Investment Hedges [Member] € in Thousands, £ in Thousands, CAD in Thousands	Sep. 30, 2017 GBP (£) DerivativeInstrument	Sep. 30, 2017 CAD DerivativeInstrument	Dec. 31, 2016 GBP (£) DerivativeInstrument	Dec. 31, 2016 EUR (€) DerivativeInstrument	Dec. 31, 2016 CAD DerivativeInstrument
EUR [Member]
Derivative [Line Items]
Number of Instruments			1	1	1
Notional Amount | €				€ 44,900
GBP [Member]
Derivative [Line Items]
Number of Instruments	1	1	2	2	2
Notional Amount | £	£ 112,700		£ 141,900
CAD [Member]
Derivative [Line Items]
Number of Instruments	1	1	2	2	2
Notional Amount | CAD		CAD 102,000			CAD 122,900