Derivative and Hedging Activities - Offsetting of Derivative Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross Amount	$ 43,049	$ 45,898
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	43,049	45,898
Credit Risk Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	10
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0
Net Amount Presented in the Balance Sheet	10
Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	2,375	2,296
Subject to Master Netting Arrangement [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	1,867	2,109
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	1,867	2,109
Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	491	140
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	491	140
Subject to Master Netting Arrangement [Member] | Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	17	47
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	17	47
Subject to Master Netting Arrangement [Member] | Credit Risk Contract [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	17	47
Not Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	40,674	43,602
Not Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	40,664	43,602
Gross Amounts Offset in the Balance Sheet, Derivative Assets	0	0
Net Amount Presented in the Balance Sheet	40,664	$ 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	$ 10