Investment Securities, AFS and HTM Securities Amortized Costs and Fair Values (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment securities available for sale:
Amortized Cost	$ 4,724,895	$ 4,984,867
Gross Unrealized Gains	19,132	35,684
Gross Unrealized Losses	(63,801)	(53,137)
Fair Value	4,680,226	4,967,414
Investment securities held to maturity:
Amortized Cost	1,273,536	1,168,230
Gross Unrealized Gains	4,523	17,505
Gross Unrealized Losses	(13,385)	(1,293)
Fair Value	1,264,674	1,184,442
U. S. Treasury securities
Investment securities available for sale:
Amortized Cost	1,000	999
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(2)
Fair Value	1,000	997
Municipal securities
Investment securities held to maturity:
Amortized Cost	1,145,843	1,043,767
Gross Unrealized Gains	3,868	16,803
Gross Unrealized Losses	(12,036)	(339)
Fair Value	1,137,675	1,060,231
Private-label
Investment securities available for sale:
Amortized Cost	1,134	1,722
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(14)	(14)
Fair Value	1,121	1,709
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
GNMA commercial mortgage-related securities
Investment securities available for sale:
Amortized Cost	2,064,508	1,982,477
Gross Unrealized Gains	356	1,334
Gross Unrealized Losses	(35,966)	(28,501)
Fair Value	2,028,898	1,955,310
Investment securities held to maturity:
Amortized Cost	0
Fair Value	0
Other securities (debt and equity)
Investment securities available for sale:
Amortized Cost	4,718	4,718
Gross Unrealized Gains	105	51
Gross Unrealized Losses	(21)	0
Fair Value	4,802	4,769
FNMA / FHLMC \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	625,234	1,388,995
Gross Unrealized Gains	17,298	33,791
Gross Unrealized Losses	(2,602)	(8,160)
Fair Value	639,930	1,414,626
Investment securities held to maturity:
Amortized Cost	37,697	41,469
Gross Unrealized Gains	439	513
Gross Unrealized Losses	(693)	(645)
Fair Value	37,443	41,337
GNMA \| Residential Related Securities
Investment securities available for sale:
Amortized Cost	2,028,301	1,605,956
Gross Unrealized Gains	1,372	507
Gross Unrealized Losses	(25,198)	(16,460)
Fair Value	2,004,475	1,590,003
Investment securities held to maturity:
Amortized Cost	89,996	82,994
Gross Unrealized Gains	216	189
Gross Unrealized Losses	(656)	(309)
Fair Value	$ 89,556	$ 82,874

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

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