Fair Value of Financial Assets and Liabilities - Offsetting of Derivative Instruments and Collateralized Transactions (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	$ 16,519	$ 23,868
Gross Amounts Offset, Assets	(951)	(517)
Net Amounts Presented in the Statements of Financial Condition, Assets	15,568	23,351
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	15,568	23,351
Gross Amounts, Liabilities	4,903	11,753
Gross Amounts Offset, Liabilities	(951)	(517)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	3,952	11,236
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	3,952	11,236
Foreign Exchange Swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	4,078	3,441
Gross Amounts Offset, Assets	(949)	(495)
Net Amounts Presented in the Statements of Financial Condition, Assets	3,129	2,946
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	3,129	2,946
Gross Amounts, Liabilities	2,689	1,472
Gross Amounts Offset, Liabilities	(949)	(495)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	1,740	977
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	1,740	977
Interest Rate Swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	245	202
Gross Amounts Offset, Assets	0	0
Net Amounts Presented in the Statements of Financial Condition, Assets	245	202
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	245	202
Foreign Exchange/Commodities Options [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	1,013	244
Gross Amounts Offset, Assets	0	0
Net Amounts Presented in the Statements of Financial Condition, Assets	1,013	244
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	1,013	244
Gross Amounts, Liabilities	313	41
Gross Amounts Offset, Liabilities	0	0
Net Amounts Presented in the Statements of Financial Condition, Liabilities	313	41
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	313	41
Forwards [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	6,438	17,881
Gross Amounts Offset, Assets	(2)	(22)
Net Amounts Presented in the Statements of Financial Condition, Assets	6,436	17,859
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	6,436	17,859
Gross Amounts, Liabilities	596	58
Gross Amounts Offset, Liabilities	(2)	(22)
Net Amounts Presented in the Statements of Financial Condition, Liabilities	594	36
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	594	36
Futures [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	67
Gross Amounts Offset, Assets	0
Net Amounts Presented in the Statements of Financial Condition, Assets	67
Gross Amounts Not Offset, Financial Instruments, Assets	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0
Net Amount, Assets	67
Gross Amounts, Liabilities	442	512
Gross Amounts Offset, Liabilities	0	0
Net Amounts Presented in the Statements of Financial Condition, Liabilities	442	512
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	442	512
Rate Lock Commitments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gross Amounts, Assets	4,678	2,100
Gross Amounts Offset, Assets	0	0
Net Amounts Presented in the Statements of Financial Condition, Assets	4,678	2,100
Gross Amounts Not Offset, Financial Instruments, Assets	0	0
Gross Amounts Not Offset, Cash Collateral Received, Assets	0	0
Net Amount, Assets	4,678	2,100
Gross Amounts, Liabilities	863	9,670
Gross Amounts Offset, Liabilities	0	0
Net Amounts Presented in the Statements of Financial Condition, Liabilities	863	9,670
Gross Amounts Not Offset, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset, Cash Collateral Received, Liabilities	0	0
Net Amount, Liabilities	$ 863	$ 9,670