Derivative Instruments and Hedging Activities - Derivative Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	$ 1,448	$ 22,037
Gross amounts not offset in the balance sheet financial instruments, derivative assets	1,448	1,378
Gross amounts not offset in the balance sheet cash collateral received, derivative assets	0	20,545
Net Amount	0	114
Interest Rate Contracts
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	228	9,256
Gross amounts not offset in the balance sheet financial instruments, derivative assets	228	843
Gross amounts not offset in the balance sheet cash collateral received, derivative assets	0	8,413
Net Amount	0	0
Interest Rate Swap
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	1,169	12,720
Gross amounts not offset in the balance sheet financial instruments, derivative assets	1,169	474
Gross amounts not offset in the balance sheet cash collateral received, derivative assets	0	12,132
Net Amount	0	114
Equity Contracts
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	51	61
Gross amounts not offset in the balance sheet financial instruments, derivative assets	51	61
Gross amounts not offset in the balance sheet cash collateral received, derivative assets	0	0
Net Amount	$ 0	$ 0