Derivative Instruments (Narrative) (Details) - Not Designated as Hedging Instrument - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Other Assets
Derivative [Line Items]
Derivative Asset	$ 7,082,000	$ 5,306,000
Interest Rate Contracts | Other Assets
Derivative [Line Items]
Derivative Asset	1,252,000	122,000
Interest Rate Contracts | Long
Derivative [Line Items]
Derivative, Notional Amount	953,600,000	1,000,000,000
Interest Rate Contracts | Short
Derivative [Line Items]
Derivative, Notional Amount	911,500,000	1,100,000,000
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations | Other Assets
Derivative [Line Items]
Derivative Asset	5,163,000	4,563,000
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations | Long
Derivative [Line Items]
Derivative, Notional Amount	168,700,000	172,400,000
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations | Short
Derivative [Line Items]
Derivative, Notional Amount	135,500,000	101,500,000
Foreign Currency Forward Contracts, Investment Operations | Other Assets
Derivative [Line Items]
Derivative Asset	40,000	408,000
Foreign Currency Forward Contracts, Investment Operations | Long
Derivative [Line Items]
Derivative, Notional Amount	13,600,000	31,300,000
Foreign Currency Forward Contracts, Investment Operations | Short
Derivative [Line Items]
Derivative, Notional Amount	112,200,000	143,400,000
Credit Default Swaps | Other Assets
Derivative [Line Items]
Derivative Asset	627,000	213,000
Credit Default Swaps | Long
Derivative [Line Items]
Derivative, Notional Amount	0	0
Credit Default Swaps | Short
Derivative [Line Items]
Derivative, Notional Amount	$ 28,400,000	$ 46,100,000