Derivatives and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	$ 7,088	$ 0
Gross Amounts of Recognized Liabilities	(1,785)	(3,830)	(98)
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative Asset	7,088	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet	1,785	3,830
Financial Instruments	0	0
Cash Collateral Received	0	0
Derivative, Fair Value, Net	5,303	(3,830)
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	7,088
Gross Amounts of Recognized Liabilities	(1,785)	(3,830)	(98)
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	7,088
Gross Amounts of Recognized Liabilities	$ (1,785)	$ (3,830)	$ (98)

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

The amount of cash received during the period on settlement of a hedge.

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- Definition

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

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- Definition

Fair value before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

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