Derivative Financial Instruments - Notional Values (Details) - Interest Rate Swaps - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	$ 5,495,857	$ 5,124,951
Trading
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	1,305,757	973,539
Cash Flow
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	1,109,933	1,106,920
Fair Value
Derivative Instruments, Gain (Loss) [Line Items]
Notional Values	$ 3,080,167	$ 3,044,492