Derivatives - Summary of Gains and Losses on Derivative Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	$ 15,481	$ 11,316	$ 26,808	$ 26,592
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	8	15	39	28
Foreign Exchange Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	142	306	1,111	563
Foreign Exchange/Commodities Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	3,004	2,735	9,632	9,292
Equity Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract		722		4,551
Futures [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	2,091	2,356	5,790	6,824
Rate Lock Commitments and Forwards [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain on derivative contract	$ 10,236	$ 5,182	$ 10,236	$ 5,334