Derivatives - Summary of Gains and Losses on Derivative Contracts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	$ 27,441	$ 17,943	$ 1,886
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	3	(48)	105
Foreign Exchange Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	987	(72)	(264)
Foreign Exchange/Commodities Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	13,312	6,294
Equity Options [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	4,551		$ 2,045
Futures [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	8,436	11,261
Forwards [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss) on derivative contract	$ 152	$ 508