Accounting Policies - Components of Other Comprehensive Income Loss and Related Tax Impact (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax		$ 56,107	$ (36,826)	$ 53,385	$ 26,778
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax		19,638	(12,890)	18,685	9,371
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax		36,469	(23,936)	34,700	17,407
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		34,202	(23,164)	29,038	17,940
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax		(500)	(200)	(1,000)	(400)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(2,901)	(5,287)	(5,635)	(10,740)
Other Comprehensive Income (Loss), before Tax		48,157	(43,771)	36,006	11,076
Other Comprehensive Income (Loss), Tax		16,856	(15,320)	12,603	3,876
Other comprehensive loss, net of tax		31,301	(28,451)	23,403	7,200
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		(3,488)	1,186	(8,710)	820
Other Comprehensive Income (Loss) before Reclassifications, Tax		(1,221)	414	(3,048)	287
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(2,267)	772	(5,662)	533
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		332	157	631	236
Other Comprehensive Income (Loss), before Tax		(2,976)	1,430	(7,739)	1,183
Other Comprehensive Income (Loss), Tax		(1,041)	501	(2,708)	414
Other comprehensive loss, net of tax		(1,935)	929	(5,031)	769
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, Net of Tax		36,469	(23,936)	34,700	17,407
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(2,585)	(3,266)	(4,961)	(6,625)
Other Comprehensive Income (Loss), before Tax		52,130	(41,851)	45,753	16,586
Other Comprehensive Income (Loss), Tax		18,246	(14,649)	16,014	5,804
Other comprehensive loss, net of tax		33,884	(27,202)	29,739	10,782
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, Net of Tax		0	0	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(648)	(2,178)	(1,305)	(4,351)
Other Comprehensive Income (Loss), before Tax		(997)	(3,350)	(2,008)	(6,693)
Other Comprehensive Income (Loss), Tax		(349)	(1,172)	(703)	(2,342)
Other comprehensive loss, net of tax		(648)	(2,178)	(1,305)	(4,351)
Gain (Loss) on Derivative Instruments [Member] | Reclassification out of Accumulated Other Comprehensive 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		(4,016)	(4,952)	(7,939)	(9,813)
Reclassification from AOCI, Current Period, Tax		(1,405)	(1,733)	(2,778)	(3,434)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(2,611)	(3,219)	(5,161)	(6,379)
Gain (Loss) on Investments [Member] | Reclassification out of Accumulated Other Comprehensive 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				9	(6)
Reclassification from AOCI, Current Period, Tax				3	(2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax				6	(4)
Other Income [Member] | Reclassification out of Accumulated Other Comprehensive 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		39	(73)	298	(373)
Reclassification from AOCI, Current Period, Tax		13	(26)	104	(131)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		26	(47)	194	(242)
Interest Income [Member] | Reclassification out of Accumulated Other Comprehensive 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	[1]	(997)	(3,350)	(2,008)	(6,693)
Reclassification from AOCI, Current Period, Tax	[1]	(349)	(1,172)	(703)	(2,342)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(648)	(2,178)	(1,305)	(4,351)
Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive 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	[2]	512	244	971	363
Reclassification from AOCI, Current Period, Tax	[2]	180	87	340	127
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[2]	$ 332	$ 157	$ 631	$ 236

[1] 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.

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