Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Amounts of Recognized Financial Instruments	$ 112,924	$ 118,846
Gross Amounts Offset in the Statement of Financial Position	(31,083)	(24,288)
Net Amounts Presented in the Statement of Financial Position	81,841	94,558
Financial Instruments/Collateral	(60,821)	(82,602)
Net Amount	21,020	11,956
Gross Amounts of Recognized Financial Instruments	29,671	21,249
Gross Amounts Offset in the Statement of Financial Position	(29,671)	(21,249)
Net Amounts Presented in the Statement of Financial Position	0	0
Financial Instruments/Collateral	0	0
Net Amount	$ 0	$ 0