Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ (7,181)	$ 53,065	$ (75,402)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(19,371)	(21,330)	(14,769)
Other Comprehensive Income (Loss), before Tax	(40,850)	48,823	(138,724)
Other Comprehensive Income (Loss), Tax	(14,298)	17,088	(48,553)
Other comprehensive income, net of tax	(26,552)	31,735	(90,171)
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	(1,776)	(559)	96
Other Comprehensive Income (Loss) before Reclassifications, Tax	(621)	(195)	33
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(1,155)	(364)	63
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	803	138	7
Other Comprehensive Income (Loss), before Tax	(541)	(347)	107
Other Comprehensive Income (Loss), Tax	(189)	(121)	37
Other comprehensive income, net of tax	(352)	(226)	70
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	(9,270)	59,887	(116,099)
Other Comprehensive Income (Loss) before Reclassifications, Tax	(3,244)	20,960	(40,634)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(6,026)	38,927	(75,465)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(13,725)	(12,939)	(14,776)
Other Comprehensive Income (Loss), before Tax	(30,387)	39,980	(138,831)
Other Comprehensive Income (Loss), Tax	(10,636)	13,992	(48,590)
Other comprehensive income, net of tax	(19,751)	25,988	(90,241)
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	22,311	0
Other Comprehensive Income (Loss) before Reclassifications, Tax	0	7,809	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	14,502	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(6,449)	(8,529)	0
Other Comprehensive Income (Loss), before Tax	(9,922)	9,190	0
Other Comprehensive Income (Loss), Tax	(3,473)	3,217	0
Other comprehensive income, net of tax	(6,449)	5,973	0
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	(20,125)	(19,213)	(19,381)
Reclassification from AOCI, Current Period, Tax	(7,044)	(6,725)	(6,783)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(13,081)	(12,488)	(12,598)
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	(10)	239	(2,114)
Reclassification from AOCI, Current Period, Tax	(4)	84	(740)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(6)	155	(1,374)
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	(982)	(933)	(1,237)
Reclassification from AOCI, Current Period, Tax	(344)	(327)	(433)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(638)	(606)	(804)
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	1,235	212	11
Reclassification from AOCI, Current Period, Tax	432	74	4
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	803	138	7
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	(9,922)	(13,121)	0
Reclassification from AOCI, Current Period, Tax	(3,473)	(4,592)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ (6,449)	$ (8,529)	$ 0