Note Offsetting of financial assets and liabilities (Offsetting of financial assets) (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative Asset Fair Value Net
Derivatives gross amount of recognized asset	$ 15,763	$ 16,719
Derivatives gross amount offset in the statement of financial position	0	0
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	15,763	16,719
Derivatives gross amount not offset financial instruments	41	121
Derivatives gross amount not offset securities collateral received	0	0
Derivatives gross amount not offset cash collateral received	0	0
Derivative Asset, Fair Value, Amount Offset Against Collateral	15,722	16,598
Offsetting Derivative Asset Securities Purchased Under Agreements To Resell Securities Borrowed [Abstract]
Total gross amount of recognized assets	15,763	16,719
Total gross amount offset in the statement of financial position	0	0
Derivative Asset Securities Purchased Under Agreements To Resell Securities Borrowed	15,763	16,719
Total gross amount not offset financial instruments	41	121
Total gross amount not offset securities collateral received	0	0
Total gross amounts not offset cash collateral received	0	0
Derivative Asset Securities Purchased Under Agreements To Resell Securities Borrowed Amount Offset Against Collateral	$ 15,722	$ 16,598