Accounting Policies - Changes in Accumulated Other Comprehensive Income, Net of Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOCI Beginning Balance	$ 15,533	$ (16,202)	$ 73,969
Other comprehensive (loss)/income before reclassifications	(7,181)	53,065	(75,402)
Amounts reclassified from AOCI	(19,371)	(21,330)	(14,769)
Net other comprehensive (loss)/income	(26,552)	31,735	(90,171)
AOCI Ending Balance	(11,019)	15,533	(16,202)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] \| Available-for-sale Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOCI Beginning Balance	9,716	(16,272)	73,969
Other comprehensive (loss)/income before reclassifications	(6,026)	38,927	(75,465)
Amounts reclassified from AOCI	(13,725)	(12,939)	(14,776)
Net other comprehensive (loss)/income	(19,751)	25,988	(90,241)
AOCI Ending Balance	(10,035)	9,716	(16,272)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest [Member] \| Held-to-maturity Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOCI Beginning Balance	5,973	0	0
Other comprehensive (loss)/income before reclassifications	0	14,502	0
Amounts reclassified from AOCI	(6,449)	(8,529)	0
Net other comprehensive (loss)/income	(6,449)	5,973	0
AOCI Ending Balance	(476)	5,973	0
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
AOCI Beginning Balance	(156)	70	0
Other comprehensive (loss)/income before reclassifications	(1,155)	(364)	63
Amounts reclassified from AOCI	803	138	7
Net other comprehensive (loss)/income	(352)	(226)	70
AOCI Ending Balance	$ (508)	$ (156)	$ 70

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
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-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 31
-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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