Offsetting of Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]
Repurchase agreements gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	$ 118,840	$ 75,324
Repurchase agreements gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	118,840	72,195
Repurchase agreements gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received		3,129
Repurchase agreements Net Amount	0	0
Gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	155,527	82,797
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	122,119	73,259
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received	32,405	8,767
Net Amount	1,003	771
Reverse repurchase agreements gross and Net Amounts of Assets Presented in the Statement of Financial Condition		118,495
Reverse repurchase agreements gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments		117,775
Reverse repurchase agreements gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received		0
Reverse repurchase agreements Net Amount		720
Gross and Net Amounts of Assets Presented in the Statement of Financial Condition		124,215
Gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments		118,839
Gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received		2,892
Net Amount		2,484
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Derivatives gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	453	587
Derivatives Net Amount	453	587
Freestanding Derivatives
Offsetting Assets and Liabilities [Line Items]
Derivatives gross and Net Amounts of Assets Presented in the Statement of Financial Condition	8,801	5,720
Derivatives gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	3,279	1,064
Derivatives gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received		2,892
Derivatives Net Amount	5,522	1,764
Derivatives gross and Net Amounts of Liabilities Presented in the Statement of Financial Condition	36,234	6,886
Derivatives gross Amounts Not Offset in the Statement of Financial Condition, Financial Instruments	3,279	1,064
Derivatives gross Amounts Not Offset in the Statement of Financial Condition, Cash Collateral Received	32,405	5,638
Derivatives Net Amount	$ 550	$ 184