Note Offsetting of financial assets and liabilities (Offsetting of financial liabilities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative Liability Fair Value Net
Derivatives gross amount of recognized liabilities	$ 14,223	$ 14,431
Derivatives gross amounts asset offset in the statement of financial position	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	14,223	14,431
Derivatives gross amount not offset financial instruments	41	121
Derivatives gross amounts not offset securities collateral received	0	8
Derivatives gross amount not offset cash collateral pledged	0	0
Derivative Liability, Fair Value, Amount Offset Against Collateral, Total	14,182	14,302
Securities Borrowed Amount Offset Against Collateral
Repurchase agreements gross amount of recognized liabilities	306,911	390,921
Repurchase agreements gross amount asset offset in the statement of financial position	0	0
Securities Sold Under Agreements To Repurchase Offsetting	306,911	390,921
Repurchase agreements gross amount not offset financial instruments	0	0
Repurchase agreeements gross amount not offset securities collateral pledged	306,911	390,921
Repurchase agreements gross amounts not offset cash collateral pledged	0	0
Securities Sold Under Agreements To Repurchase Amount Offset Against Collateral	0	0
Offsetting Derivative Liability Securities Sold Under Agreements To Resell Securities Loaned
Total gross amount of recognized liabilities	321,134	405,352
Total gross amounts of asset offset in the statement of financial position	0	0
Derivative Liability Securities Sold Under Agreements To Resell Securities Loaned	321,134	405,352
Total gross amounts not offset financial instruments	41	121
Total gross amounts not offset securities collateral pledged	306,911	390,929
Total gross amounts not offset cash collateral pledged	0	0
Derivative Liability Securities Sold Under Agreements To Resell Securities Loaned Amount Offset Against Collateral	$ 14,182	$ 14,302