Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) (Fair Value Measurements Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Non-derivative Assets:
Assets, fair value disclosure, Total	$ 44,686	$ 29,620
Non-derivative liabilities
Liabilities, fair value disclosure, Total	(4,302)	(3,764)
Assets and liabilities, fair value disclosure	40,384	25,856
Equity and U.S Treasury Securities [Member]
Non-derivative Assets:
Non-derivative assets	43,504	29,041
Margin Account Balance [Member]
Non-derivative liabilities
Non-derivative Liabilities:	(3,867)	(3,130)
Interest Rate Derivatives [Member] | Not Designated As Hedging Instrument [Member]
Derivative Assets:
Derivative assets	312	19
Call Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	(156)	(479)
Credit Default Swaps [Member]
Derivative Assets:
Derivative assets	101
Derivative Liabilities:
Derivative liabilities		(73)
Put and Call Options [Member]
Derivative Assets:
Derivative assets	769	560
Put Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	(279)	(82)
Quoted Market Prices (Level 1) [Member]
Non-derivative Assets:
Assets, fair value disclosure, Total	44,273	29,601
Non-derivative liabilities
Liabilities, fair value disclosure, Total	(4,302)	(3,691)
Assets and liabilities, fair value disclosure	39,971	25,910
Quoted Market Prices (Level 1) [Member] | Equity and U.S Treasury Securities [Member]
Non-derivative Assets:
Non-derivative assets	43,504	29,041
Quoted Market Prices (Level 1) [Member] | Margin Account Balance [Member]
Non-derivative liabilities
Non-derivative Liabilities:	(3,867)	(3,130)
Quoted Market Prices (Level 1) [Member] | Interest Rate Derivatives [Member] | Not Designated As Hedging Instrument [Member]
Derivative Assets:
Derivative assets	0	0
Quoted Market Prices (Level 1) [Member] | Call Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	(156)	(479)
Quoted Market Prices (Level 1) [Member] | Credit Default Swaps [Member]
Derivative Assets:
Derivative assets	0
Derivative Liabilities:
Derivative liabilities		0
Quoted Market Prices (Level 1) [Member] | Put and Call Options [Member]
Derivative Assets:
Derivative assets	769	560
Quoted Market Prices (Level 1) [Member] | Put Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	(279)	(82)
Significant Other Observable Inputs (Level 2) [Member]
Non-derivative Assets:
Assets, fair value disclosure, Total	976	19
Non-derivative liabilities
Liabilities, fair value disclosure, Total	0	995
Assets and liabilities, fair value disclosure	976	1,014
Significant Other Observable Inputs (Level 2) [Member] | Equity and U.S Treasury Securities [Member]
Non-derivative Assets:
Non-derivative assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Margin Account Balance [Member]
Non-derivative liabilities
Non-derivative Liabilities:	0	0
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Derivatives [Member] | Not Designated As Hedging Instrument [Member]
Derivative Assets:
Derivative assets	312	19
Significant Other Observable Inputs (Level 2) [Member] | Call Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Credit Default Swaps [Member]
Derivative Assets:
Derivative assets	664
Derivative Liabilities:
Derivative liabilities		995
Significant Other Observable Inputs (Level 2) [Member] | Put and Call Options [Member]
Derivative Assets:
Derivative assets	0	0
Significant Other Observable Inputs (Level 2) [Member] | Put Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	0	0
Counterparty and Cash Collateral Netting [Member]
Non-derivative Assets:
Assets, fair value disclosure, Total	(563)	0
Non-derivative liabilities
Liabilities, fair value disclosure, Total	0	(1,068)
Assets and liabilities, fair value disclosure	(563)	(1,068)
Counterparty and Cash Collateral Netting [Member] | Equity and U.S Treasury Securities [Member]
Non-derivative Assets:
Non-derivative assets	0	0
Counterparty and Cash Collateral Netting [Member] | Margin Account Balance [Member]
Non-derivative liabilities
Non-derivative Liabilities:	0	0
Counterparty and Cash Collateral Netting [Member] | Interest Rate Derivatives [Member] | Not Designated As Hedging Instrument [Member]
Derivative Assets:
Derivative assets	0	0
Counterparty and Cash Collateral Netting [Member] | Call Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	0	0
Counterparty and Cash Collateral Netting [Member] | Credit Default Swaps [Member]
Derivative Assets:
Derivative assets	(563)
Derivative Liabilities:
Derivative liabilities		(1,068)
Counterparty and Cash Collateral Netting [Member] | Put and Call Options [Member]
Derivative Assets:
Derivative assets	0	0
Counterparty and Cash Collateral Netting [Member] | Put Option [Member] | Short [Member]
Derivative Liabilities:
Derivative liabilities	$ 0	$ 0