Securities (Schedule of Available-for-sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	$ 2,787,893
Gross Unrealized Gains	1,609
Gross Unrealized Losses	(112,992)
Available-for-sale debt securities, Fair Value	2,676,510
Available-for-sale debt and equity investment securities, Amortized Cost		$ 3,070,067
Available-for-sale debt and equity investment securities, Gross Unrealized Gains		5,013
Available-for-sale debt and equity investment securities, Gross Unrealized Losses		(58,328)
Available-for-sale debt and equity securities, Fair Value		3,016,752
U.S. Treasury securities
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	625,449	651,395
Gross Unrealized Gains	18	0
Gross Unrealized Losses	(21,541)	(11,115)
Available-for-sale debt securities, Fair Value	603,926	640,280
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	235,165	206,815
Gross Unrealized Gains	0	62
Gross Unrealized Losses	(6,509)	(3,485)
Available-for-sale debt securities, Fair Value	228,656	203,392
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	382,048	328,348
Gross Unrealized Gains	0	141
Gross Unrealized Losses	(16,978)	(9,532)
Available-for-sale debt securities, Fair Value	365,070	318,957
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	931,107	1,199,869
Gross Unrealized Gains	1,530	3,964
Gross Unrealized Losses	(29,188)	(13,562)
Available-for-sale debt securities, Fair Value	903,449	1,190,271
Municipal securities
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	74,261	99,636
Gross Unrealized Gains	61	655
Gross Unrealized Losses	(1,498)	(309)
Available-for-sale debt securities, Fair Value	72,824	99,982
Non-agency commercial mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	16,030
Gross Unrealized Gains	0
Gross Unrealized Losses	(104)
Available-for-sale debt securities, Fair Value	15,926
Non-agency residential mortgage-backed securities \| Investment grade
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	10,606	9,136
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(244)	(22)
Available-for-sale debt securities, Fair Value	10,362	9,117
Corporate debt securities \| Investment grade
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	11,250	37,585
Gross Unrealized Gains	0	164
Gross Unrealized Losses	(308)	(746)
Available-for-sale debt securities, Fair Value	10,942	37,003
Foreign bonds \| Investment grade
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	489,367	505,396
Gross Unrealized Gains	0	24
Gross Unrealized Losses	(36,524)	(19,012)
Available-for-sale debt securities, Fair Value	452,843	486,408
Foreign bonds \| Investment grade \| Multilateral development bank
Schedule of Available-for-sale Securities
Available-for-sale debt securities, Fair Value	438,400	456,100
Asset-backed securities \| Investment grade
Schedule of Available-for-sale Securities
Total available-for-sale debt securities, Amortized Cost	12,610
Gross Unrealized Gains	0
Gross Unrealized Losses	(98)
Available-for-sale debt securities, Fair Value	$ 12,512
Other securities
Schedule of Available-for-sale Securities
Other securities, Amortized Cost		31,887
Other securities, Gross Unrealized Gains		0
Other securities, Gross Unrealized Losses		(545)
Other securities, Fair Value		$ 31,342

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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