Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Off-Balance Sheet Guaranteed Securities (Details) - Guarantor Obligations, Nature [Domain] - Variable Interest Entity, Not Primary Beneficiary [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 1,573,228	$ 1,636,592
Farm & Ranch [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	575,811	636,086
USDA Guarantees [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	10,888	13,978
Institutional Credit [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 986,529	$ 986,528