Investments (Aggregate Values and Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	$ 280,126	$ 832,420
Investment securities available for sale
Cost	6,885,797	7,163,574
Gross Unrealized Gains	6,367	20,589
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	30,871	12,246
Fair Value	6,861,293	7,171,917
Investment securities held to maturity
Cost	255	518
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,094	10,043
U. S. Treasury
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	0	1,015
Investment securities available for sale
Cost	1,675,996	2,626,900
Gross Unrealized Gains	4	2,922
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,118	152
Fair Value	1,674,882	2,629,670
Investment securities held to maturity
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1
Government Agency
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	0	0
Investment securities available for sale
Cost	498,804	908,362
Gross Unrealized Gains	230	702
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	374	247
Fair Value	498,660	908,817
Investment securities held to maturity
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Mortgage Backed Securities, Other
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	280,126	831,405
Investment securities available for sale
Cost	4,692,447	3,628,187
Gross Unrealized Gains	5,120	16,964
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	29,369	11,847
Fair Value	4,668,198	3,633,304
Investment securities held to maturity
Cost	255	518
Held To Maturity Securities Accumulated Unrecognized Holding Gain	10	26
Held To Maturity Securities Accumulated Unrecognized Holding Loss	0	0
Fair Value	265	544
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6,094	10,042
Equity Securities
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	0
Investment securities available for sale
Cost	7,935
Gross Unrealized Gains	968
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	10
Fair Value	8,893
Investment securities held to maturity
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
State, County and Municipal
Investment securities available for sale
Cost		125
Gross Unrealized Gains		1
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments		0
Fair Value		$ 126
Other Debt Obligations
Schedule of Investments [Line Items]
Aggregate fair value, continuous unrealized loss position, 12 months or more	0
Investment securities available for sale
Cost	10,615
Gross Unrealized Gains	45
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0
Fair Value	10,660
Investment securities held to maturity
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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