Investments (Unrealized Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment securities available for sale:
Less than 12 months, fair value	$ 5,257,891	$ 5,340,271
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments	83,342	24,777
Aggregate fair value, continuous unrealized loss position, 12 months or more	362,351	280,126
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,689	6,094
Total fair value	5,620,242	5,620,397
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	88,031	30,871
U. S. Treasury
Investment securities available for sale:
Less than 12 months, fair value	807,822	1,539,637
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments	935	1,118
Aggregate fair value, continuous unrealized loss position, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total fair value	807,822	1,539,637
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	935	1,118
Government Agency
Investment securities available for sale:
Less than 12 months, fair value		229,436
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments		374
Aggregate fair value, continuous unrealized loss position, 12 months or more		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Total fair value		229,436
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	374
Mortgage Backed Securities, Other
Investment securities available for sale:
Less than 12 months, fair value	4,442,700	3,570,470
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments	82,161	23,275
Aggregate fair value, continuous unrealized loss position, 12 months or more	362,351	280,126
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,689	6,094
Total fair value	4,805,051	3,850,596
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	86,850	29,369
Equity Securities
Investment securities available for sale:
Less than 12 months, fair value		728
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments		10
Aggregate fair value, continuous unrealized loss position, 12 months or more		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0
Total fair value		728
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	10
Other Debt Obligations
Investment securities available for sale:
Less than 12 months, fair value	7,369
Available for Sale Securities Continuous Unrealized Loss Position Less Than 12 Months Aggregate Losses Accumulated In Investments	246
Aggregate fair value, continuous unrealized loss position, 12 months or more	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Total fair value	7,369
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	$ 246	$ 0

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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