Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Amounts of Recognized Financial Instruments	$ 153,491	$ 118,846
Gross Amounts Offset in the Statement of Financial Position	(18,608)	(24,288)
Net Amounts Presented in the Statement of Financial Position	134,883	94,558
Financial Instruments/Collateral	(131,034)	(82,602)
Net Amount	3,849	11,956
Gross Amounts of Recognized Financial Instruments	24,482	21,249
Gross Amounts Offset in the Statement of Financial Position	(24,482)	(21,249)
Net Amounts Presented in the Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0