Investments (Maturity Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment securities available for sale
Total investment securities available for sale, cost	$ 7,079,287	$ 6,885,797
Investment securities available for sale	7,006,580	6,861,293
Investment securities held to maturity
Investment securities held to maturity	98	255
Debt Securities
Investment securities available for sale
Maturing in one year or less, cost	842,798	1,255,714
Maturing in one through five years, cost	848,168	919,086
Maturing in five through ten years, cost	49,367	8,500
Maturing in over ten years, cost	7,615	2,115
Maturing in one year or less, fair value	842,947	1,255,094
Maturing in one through five years, fair value	847,770	918,448
Maturing in five through ten years, fair value	49,562	8,500
Maturing in over ten years, fair value	7,369	2,160
Equity Securities
Investment securities available for sale
Total investment securities available for sale, cost	71,873	7,935
Investment securities available for sale	83,507	8,893
Mortgage Backed Securities, Other
Investment securities available for sale
Total investment securities available for sale, cost	5,259,466	4,692,447
Investment securities available for sale	5,175,425	4,668,198
Investment securities held to maturity
Investment securities held to maturity	98	255
Fair Value	$ 104	$ 265

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

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