Investment Securities, AFS and HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Available for Sale, Due in one year or less	$ 8,343
Available for Sale, Due after one year through five years	82,198
Available for Sale, Due after five years through ten years	344,172
Available for Sale, Due after ten years	69,987
Available for Sale, Total debt securities	504,699
Available for Sale, amortized cost	3,203,046	$ 3,251,950
Fair Value
Available for Sale, Due in one year or less	8,350
Available for Sale, Due after one year through five years	82,964
Available for Sale, Due after five years through ten years	362,247
Available for Sale, Due after ten years	75,815
Available for Sale, Total debt securities	529,375
Investment securities available for sale, at fair value	$ 3,258,360	3,262,586
Available for Sale, Ratio of Fair Value to Amortized Cost	101.70%
Amortized Cost
Held to Maturity, Due in one year or less	$ 28,957
Held to Maturity, Due after one year through five years	63,630
Held to Maturity, Due after five years through ten years	161,769
Held to Maturity, Due after ten years	1,190,968
Held to Maturity, Total Debt Securities	1,445,325
Held to Maturity, Amortized Cost	1,990,940	2,205,083
Fair Value
Held to Maturity, Due in one year or less	29,140
Held to Maturity, Due after one year through five years	65,751
Held to Maturity, Due after five years through ten years	170,223
Held to Maturity, Due after ten years	1,295,217
Held to Maturity, Securities, Debt Securities	1,560,331
Held to Maturity, Total debt securities at fair value	$ 2,124,452	2,276,465
Held to Maturity, Ratio of Fair Value to Amortized Cost	106.70%
SBA
Amortized Cost
Available for Sale, amortized cost	$ 9,159
Fair Value
Investment securities available for sale, at fair value	9,111
Amortized Cost
Held to Maturity, Amortized Cost	0
Fair Value
Held to Maturity, Total debt securities at fair value	0
FFELP
Amortized Cost
Available for Sale, amortized cost	332,398	270,178
Fair Value
Investment securities available for sale, at fair value	325,843	263,693
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	1,267,003	131,158
Fair Value
Investment securities available for sale, at fair value	1,276,463	132,660
Amortized Cost
Held to Maturity, Amortized Cost	63,142	81,676
Fair Value
Held to Maturity, Total debt securities at fair value	66,289	83,420
FNMA/FHLMC \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, amortized cost	19,724	19,929
Fair Value
Investment securities available for sale, at fair value	21,877	21,728
Amortized Cost
Held to Maturity, Amortized Cost	11,220
Fair Value
Held to Maturity, Total debt securities at fair value	11,220
GNMA \| Residential Related Securities
Amortized Cost
Available for Sale, amortized cost	399,490	982,941
Fair Value
Investment securities available for sale, at fair value	407,313	985,139
Amortized Cost
Held to Maturity, Amortized Cost	159,455	269,523
Fair Value
Held to Maturity, Total debt securities at fair value	164,672	270,296
GNMA \| Commercial mortgage-related securities
Amortized Cost
Available for Sale, amortized cost	670,573	1,314,836
Fair Value
Investment securities available for sale, at fair value	688,378	1,310,207
Amortized Cost
Held to Maturity, Amortized Cost	311,798	434,317
Fair Value
Held to Maturity, Total debt securities at fair value	$ 321,941	$ 434,503

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

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