Investments (Aggregate Values and Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment securities available for sale
Cost	$ 6,663,652	$ 7,163,574
Gross Unrealized Gains	33,845	20,589
Gross Unrealized Losses	6,919	12,246
Fair Value	6,690,578	7,171,917
Investment securities held to maturity
Cost	301	518
U. S. Treasury
Investment securities available for sale
Cost	1,685,794	2,626,900
Gross Unrealized Gains	5,708	2,922
Gross Unrealized Losses	0	152
Fair Value	1,691,502	2,629,670
Government Agency
Investment securities available for sale
Cost	633,162	908,362
Gross Unrealized Gains	1,742	702
Gross Unrealized Losses	0	247
Fair Value	634,904	908,817
Mortgage Backed Securities
Investment securities available for sale
Cost	4,343,105	3,628,187
Gross Unrealized Gains	26,375	16,964
Gross Unrealized Losses	6,919	11,847
Fair Value	4,362,561	3,633,304
Investment securities held to maturity
Cost	301	518
Held To Maturity Securities Accumulated Unrecognized Holding Gain	13	26
Held To Maturity Securities Accumulated Unrecognized Holding Loss	0	0
Fair Value	314	544
Equity Securities
Investment securities available for sale
Cost	1,591
Gross Unrealized Gains	20
Gross Unrealized Losses	0
Fair Value	$ 1,611
State, County and Municipal
Investment securities available for sale
Cost		125
Gross Unrealized Gains		1
Gross Unrealized Losses		0
Fair Value		$ 126

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

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

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