Derivative Instruments - Derivative Assets (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	$ 39,238	$ 33,317
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets	862	53
Net Amount, Derivative Assets	94	82
Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	1,736	3,579
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets	780	3,444
Counterparty B [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets
Counterparty B [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet		24
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets		24
Counterparty D [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets
Counterparty D [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	56	566
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets	56	566
Counterparty E [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets
Counterparty E [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	476	1,696
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets	476	1,696
Counterparty F [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets	94	82
Counterparty F [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	94	355
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets		273
Counterparty G [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets
Counterparty G [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	50	251
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets	50	251
Counterparty I [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets
Net Amount, Derivative Assets
Counterparty I [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	198	634
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets	198	634
Counterparty J [Member]
Derivative [Line Items]
Gross Amounts Not Offset in the Balance Sheet Cash Collateral Received, Derivative Assets	862	53
Net Amount, Derivative Assets
Counterparty J [Member] | Derivative Assets Subject to Master Netting Arrangement [Member]
Derivative [Line Items]
Net Amount Presented in the Balance Sheet	862	53
Gross Amounts Not Offset in the Balance Sheet Financial Instruments, Derivative Assets