Investments (Aggregate Values and Unrealized Gains and Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment securities available for sale
Cost	$ 4,607,117	$ 7,229,014
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	6,425	32,094
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	56,432	80,928
Fair Value	4,557,110	7,180,180
Investment securities held to maturity
Cost	2,184,653	76
U. S. Treasury
Investment securities available for sale
Cost	1,249,243	1,658,410
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	633	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,166	546
Fair Value	1,247,710	1,657,864
Government Agency
Investment securities available for sale
Cost	257,252	8,695
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	222	15
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	639	40
Fair Value	256,835	8,670
Mortgage Backed Securities
Investment securities available for sale
Cost	2,956,793	5,419,379
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	5,309	1,529
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	52,763	80,152
Fair Value	2,909,339	5,340,756
Investment securities held to maturity
Cost	2,184,653	76
Held To Maturity Securities Accumulated Unrecognized Holding Gain	17,339	5
Held To Maturity Securities Accumulated Unrecognized Holding Loss	490	0
Fair Value	2,201,502	81
Equity Securities
Investment securities available for sale
Cost		75,471
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		29,737
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments		0
Fair Value		105,208
Corporate Bonds
Investment securities available for sale
Cost	139,906	59,414
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	59	557
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	864	8
Fair Value	139,101	59,963
Other Debt Obligations
Investment securities available for sale
Cost	3,923	7,645
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	202	256
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	182
Fair Value	$ 4,125	$ 7,719

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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