Derivatives - Offsetting of Derivative Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Offsetting Assets [Line Items]
Gross Amounts, Assets	$ 258,490	$ 119,466
Gross Amounts Offset, Assets	(206,933)	(106,797)
Net Amounts Presented in the Statements of Financial Condition, Assets	51,557	12,669
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	51,557	12,669
Gross Amounts, Liabilities	259,081	114,730
Gross Amounts Offset, Liabilities	(206,933)	(106,797)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	52,148	7,933
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	52,148	7,933
Foreign Exchange Swaps [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets	1,399	1,135
Gross Amounts Offset, Assets	(503)	(334)
Net Amounts Presented in the Statements of Financial Condition, Assets	896	801
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	896	801
Gross Amounts, Liabilities	2,578	3,180
Gross Amounts Offset, Liabilities	(503)	(334)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	2,075	2,846
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	2,075	2,846
Foreign Exchange/Commodities Options [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets	192,311	31,834
Gross Amounts Offset, Assets	(192,174)	(27,418)
Net Amounts Presented in the Statements of Financial Condition, Assets	137	4,416
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	137	4,416
Gross Amounts, Liabilities	226,023	27,548
Gross Amounts Offset, Liabilities	(192,174)	(27,418)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	33,849	130
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	33,849	130
Interest Rate Swaps [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets		242
Gross Amounts Offset, Assets		0
Net Amounts Presented in the Statements of Financial Condition, Assets		242
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets		242
Equity Options [Member]
Offsetting Assets [Line Items]
Gross Amounts, Liabilities		18
Gross Amounts Offset, Liabilities		0
Net Amounts Presented in the Statements of Financial Condition, Liabilities		18
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities		18
Forwards [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets	36,022	4,363
Gross Amounts Offset, Assets	(105)	(101)
Net Amounts Presented in the Statements of Financial Condition, Assets	35,917	4,262
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	35,917	4,262
Gross Amounts, Liabilities	1,752	1,584
Gross Amounts Offset, Liabilities	(105)	(101)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	1,647	1,483
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	1,647	1,483
Rate Lock Commitments [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets	14,448	2,923
Gross Amounts Offset, Assets		0
Net Amounts Presented in the Statements of Financial Condition, Assets	14,448	2,923
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	14,448	2,923
Gross Amounts, Liabilities	13,945	2,390
Gross Amounts Offset, Liabilities		0
Net Amounts Presented in the Statements of Financial Condition, Liabilities	13,945	2,390
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	13,945	2,390
Futures [Member]
Offsetting Assets [Line Items]
Gross Amounts, Assets	14,310	78,969
Gross Amounts Offset, Assets	(14,151)	(78,944)
Net Amounts Presented in the Statements of Financial Condition, Assets	159	25
Gross Amounts Not Offset, Financial Instruments, Assets		0
Gross Amounts Not Offset, Cash Collateral Received, Assets		0
Net Amount, Assets	159	25
Gross Amounts, Liabilities	14,783	80,010
Gross Amounts Offset, Liabilities	(14,151)	(78,944)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	632	1,066
Gross Amounts Not Offset, Financial Instruments, Liabilities		0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities		0
Net Amount, Liabilities	$ 632	$ 1,066