Derivative and Hedging Activities - Offsetting of Derivative Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Gross Amount	$ 43,319	$ 46,160
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0	0
Net Amount Presented in the Balance Sheet	43,319	46,160
Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	16
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0
Net Amount Presented in the Balance Sheet	16
Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	42,812	45,985
Subject to Master Netting Arrangement [Member] | Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	1,869	2,330
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0	0
Net Amount Presented in the Balance Sheet	1,869	2,330
Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	40,943	43,655
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0	0
Net Amount Presented in the Balance Sheet	40,943	43,655
Not Subject to Master Netting Arrangement [Member]
Derivatives, Fair Value [Line Items]
Net Amount Presented in the Balance Sheet	507	175
Not Subject to Master Netting Arrangement [Member] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	377	128
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0	0
Net Amount Presented in the Balance Sheet	377	128
Not Subject to Master Netting Arrangement [Member] | Equity Contracts [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		47
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities		0
Net Amount Presented in the Balance Sheet	16	$ 47
Not Subject to Master Netting Arrangement [Member] | Credit Risk Contract [Member]
Derivatives, Fair Value [Line Items]
Gross Amount	114
Gross Amounts Offset in the Balance Sheet, Derivative Liabilities	0
Net Amount Presented in the Balance Sheet	$ 114