Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		$ (5,164)	$ 41,106
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		500	119
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(2,734)	(5,455)
Other Comprehensive Income (Loss), before Tax		(12,151)	54,847
Other Comprehensive Income (Loss), Tax		(4,253)	19,196
Other comprehensive loss, net of tax		(7,898)	35,651
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		(5,222)	(366)
Other Comprehensive Income (Loss) before Reclassifications, Tax		(1,827)	(129)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(3,395)	(237)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		299	77
Other Comprehensive Income (Loss), before Tax		(4,763)	(247)
Other Comprehensive Income (Loss), Tax		(1,667)	(87)
Other comprehensive loss, net of tax		(3,096)	(160)
Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		(2,722)	63,604
Other Comprehensive Income (Loss) before Reclassifications, Tax		(953)	22,261
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(1,769)	41,343
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(2,376)	(3,359)
Other Comprehensive Income (Loss), before Tax		(6,377)	58,437
Other Comprehensive Income (Loss), Tax		(2,232)	20,453
Other comprehensive loss, net of tax		(4,145)	37,984
Held-to-maturity Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, before Tax		0	0
Other Comprehensive Income (Loss) before Reclassifications, Tax		0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(657)	(2,173)
Other Comprehensive Income (Loss), before Tax		(1,011)	(3,343)
Other Comprehensive Income (Loss), Tax		(354)	(1,170)
Other comprehensive loss, net of tax		(657)	(2,173)
Gain (Loss) on Derivative Instruments [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1]	(3,923)	(4,861)
Reclassification from AOCI, Current Period, Tax	[1]	(1,373)	(1,701)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(2,550)	(3,160)
Gain (Loss) on Investments [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[2]	9	(6)
Reclassification from AOCI, Current Period, Tax	[2]	3	(2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[2]	6	(4)
Other Income [Member] | Available-for-sale Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[3]	259	(300)
Reclassification from AOCI, Current Period, Tax	[3]	91	(105)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[3]	168	(195)
Interest Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[4]	459	119
Reclassification from AOCI, Current Period, Tax	[4]	160	42
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[4]	299	77
Interest Income [Member] | Held-to-maturity Securities [Member] | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[5]	(1,011)	(3,343)
Reclassification from AOCI, Current Period, Tax	[5]	(354)	(1,170)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[5]	$ (657)	$ (2,173)

[1] (1) Relates to the amortization of unrealized gains on hedged items prior to the application of fair value hedge accounting.

[2] (2) Represents unrealized gains and losses on sales of available-for-sale investment securities.

[3] (3) Represents amortization of deferred gains related to certain available-for-sale USDA Securities and Farmer Mac Guaranteed USDA Securities.

[4] (5) Relates to the recognition of unrealized gains and losses on cash flow hedges recorded in AOCI.

[5] (4) Relates to the amortization of unrealized gains or losses prior to the reclassification of these securities from available-for-sale to held-to-maturity. The amortization of unrealized gains or losses reported in AOCI for held-to-maturity securities will be offset by the amortization of the premium or discount created from the transfer into held-to-maturity securities, which occurred at fair value. These unrealized gains or losses will be recorded over the remaining life of the security with no impact on future net income.