Investments (Maturity Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment securities available for sale
Total investment securities available for sale, cost	$ 4,607,117	$ 7,229,014
Investment securities available for sale	4,557,110	7,180,180
Investment securities held to maturity
Investment securities held to maturity	2,184,653	76
Debt Securities
Investment securities available for sale
Maturing in one year or less, cost	1,049,253	808,768
Maturing in one through five years, cost	205,526	849,642
Maturing in five through ten years, cost	134,370	59,414
Maturing in over ten years, cost	3,923	7,645
Maturing in one year or less, fair value	1,047,380	808,301
Maturing in one through five years, fair value	205,805	849,563
Maturing in five through ten years, fair value	133,626	59,963
Maturing in over ten years, fair value	4,125	7,719
Equity Securities
Investment securities available for sale
Total investment securities available for sale, cost	0	75,471
Investment securities available for sale	0	105,208
Government Agency
Investment securities available for sale
Total investment securities available for sale, cost	257,252	8,695
Investment securities available for sale	256,835	8,670
Mortgage Backed Securities
Investment securities available for sale
Total investment securities available for sale, cost	2,956,793	5,419,379
Investment securities available for sale	2,909,339	5,340,756
Investment securities held to maturity
Investment securities held to maturity	2,184,653	76
Fair Value	$ 2,201,502	$ 81

Amortized cost of 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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