Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amortized Cost
Available for Sale, Due in one year or less	$ 1,000
Available for Sale, Due after one year through five years	2,000
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	3,000
Available for Sale, amortized cost	3,290,593	$ 4,041,902
Fair Value
Available for Sale, Due in one year or less	1,000
Available for Sale, Due after one year through five years	2,000
Available for Sale, Due after five years through ten years	0
Available for Sale, Due after ten years	0
Available for Sale, Total debt securities	3,000
Investment securities available for sale, at fair value	$ 3,283,456	3,946,941
Available for Sale, Ratio of Fair Value to Amortized Cost	99.80%
Amortized Cost
Held to Maturity, Due in one year or less	$ 48,235
Held to Maturity, Due after one year through five years	184,581
Held to Maturity, Due after five years through ten years	479,215
Held to Maturity, Due after ten years	1,202,705
Held to Maturity, Total Debt Securities	1,914,735
Held to Maturity, Amortized Cost	2,806,064	2,740,511
Fair Value
Held to Maturity, Due in one year or less	48,393
Held to Maturity, Due after one year through five years	185,909
Held to Maturity, Due after five years through ten years	491,122
Held to Maturity, Due after ten years	1,257,552
Held to Maturity, Securities, Debt Securities	1,982,976
Held to Maturity, Total debt securities at fair value	$ 2,874,758	2,710,271
Held to Maturity, Ratio of Fair Value to Amortized Cost	102.40%
Private-label
Amortized Cost
Available for Sale, amortized cost	$ 805	1,007
Fair Value
Investment securities available for sale, at fair value	814	1,003
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
FFELP asset backed securities
Amortized Cost
Available for Sale, amortized cost	274,520	297,347
Fair Value
Investment securities available for sale, at fair value	273,137	297,360
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
FNMA/FHLMC \| Residential Related Securities
Amortized Cost
Available for Sale, amortized cost	182,893	296,296
Fair Value
Investment securities available for sale, at fair value	183,722	295,252
Amortized Cost
Held to Maturity, Amortized Cost	89,078	92,788
Fair Value
Held to Maturity, Total debt securities at fair value	90,076	91,162
FNMA/FHLMC \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, amortized cost	20,244
Fair Value
Investment securities available for sale, at fair value	21,102
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
GNMA \| Residential Related Securities
Amortized Cost
Available for Sale, amortized cost	1,325,739	2,169,943
Fair Value
Investment securities available for sale, at fair value	1,331,633	2,128,531
Amortized Cost
Held to Maturity, Amortized Cost	321,046	351,606
Fair Value
Held to Maturity, Total debt securities at fair value	324,184	345,035
GNMA \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, amortized cost	1,483,392	1,273,309
Fair Value
Investment securities available for sale, at fair value	1,470,048	1,220,797
Amortized Cost
Held to Maturity, Amortized Cost	481,205	505,434
Fair Value
Held to Maturity, Total debt securities at fair value	$ 477,521	$ 490,414

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Ratio of Fair Value to Amortized Cost, AFS

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

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-SubTopic 320
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803

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-SubTopic 10
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