Derivative Instruments - Offsetting of Derivative Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross Amount	$ 53,202	$ 45,898
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	53,202	45,898
Credit Risk Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	7
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0
Net Amount Presented in the Balance Sheet	7
Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	3,197	2,296
Subject to Master Netting Arrangement [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	3,178	2,109
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	3,178	2,109
Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	1	140
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	1	140
Subject to Master Netting Arrangement [Member] | Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	18	47
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	18	47
Not Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	50,005	43,602
Not Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	49,998	43,602
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	49,998	$ 43,602
Not Subject to Master Netting Arrangement [Member] | Credit Risk Contract [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	$ 7