Derivatives - Summary of Gains and Losses on Derivative Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	$ 5,119	$ 7,310	$ 11,326	$ 11,891
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	3	9	31	13
Foreign Exchange Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	342	137	969	257
Foreign Exchange/Commodities Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	3,025	3,281	6,628	6,410
Equity Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract		3,317		3,761
Futures [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	$ 1,749	$ 566	$ 3,698	1,298
Forwards [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract				$ 152