Securities (Schedule of Available-for-sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale investment securities:
Amortized Cost	$ 2,890,893	$ 3,070,067
Gross Unrealized Gains	2,711	5,013
Gross Unrealized Losses	(82,188)	(58,328)
Fair Value	2,811,416	3,016,752
U.S. Treasury securities
Available-for-sale investment securities:
Amortized Cost	668,670	651,395
Gross Unrealized Gains	93	0
Gross Unrealized Losses	(16,933)	(11,115)
Fair Value	651,830	640,280
U.S. government agency and U.S. government sponsored enterprise debt securities
Available-for-sale investment securities:
Amortized Cost	235,776	206,815
Gross Unrealized Gains	175	62
Gross Unrealized Losses	(2,935)	(3,485)
Fair Value	233,016	203,392
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Available-for-sale investment securities:
Amortized Cost	352,980	328,348
Gross Unrealized Gains	170	141
Gross Unrealized Losses	(13,316)	(9,532)
Fair Value	339,834	318,957
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Available-for-sale investment securities:
Amortized Cost	1,008,235	1,199,869
Gross Unrealized Gains	1,844	3,964
Gross Unrealized Losses	(20,626)	(13,562)
Fair Value	989,453	1,190,271
Municipal securities
Available-for-sale investment securities:
Amortized Cost	74,942	99,636
Gross Unrealized Gains	251	655
Gross Unrealized Losses	(1,117)	(309)
Fair Value	74,076	99,982
Non-agency residential mortgage-backed securities \| Investment grade
Available-for-sale investment securities:
Amortized Cost	8,547	9,136
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(143)	(22)
Fair Value	8,404	9,117
Corporate debt securities \| Investment grade
Available-for-sale investment securities:
Amortized Cost	36,379	37,585
Gross Unrealized Gains	178	164
Gross Unrealized Losses	(699)	(746)
Fair Value	35,858	37,003
Foreign bonds \| Investment grade
Available-for-sale investment securities:
Amortized Cost	505,364	505,396
Gross Unrealized Gains	0	24
Gross Unrealized Losses	(26,419)	(19,012)
Fair Value	478,945	486,408
Foreign bonds \| Investment grade \| Multilateral development bank
Available-for-sale investment securities:
Fair Value	$ 448,500	456,100
Other securities
Available-for-sale investment securities:
Amortized Cost		31,887
Gross Unrealized Gains		0
Gross Unrealized Losses		(545)
Fair Value		$ 31,342

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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