Securities (Schedule of Available-for-sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	$ 2,806,900
Gross Unrealized Gains	5,714
Gross Unrealized Losses	(70,767)
Available-for-sale debt securities, Fair Value	2,741,847
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, Fair Value		3,016,752
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	577,561	651,395
Gross Unrealized Gains	153	0
Gross Unrealized Losses	(12,899)	(11,115)
Available-for-sale debt securities, Fair Value	564,815	640,280
U.S. government agency and U.S. government sponsored enterprise debt securities
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	219,485	206,815
Gross Unrealized Gains	382	62
Gross Unrealized Losses	(2,694)	(3,485)
Available-for-sale debt securities, Fair Value	217,173	203,392
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	420,486	328,348
Gross Unrealized Gains	811	141
Gross Unrealized Losses	(12,694)	(9,532)
Available-for-sale debt securities, Fair Value	408,603	318,957
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	957,219	1,199,869
Gross Unrealized Gains	4,026	3,964
Gross Unrealized Losses	(14,552)	(13,562)
Available-for-sale debt securities, Fair Value	946,693	1,190,271
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	82,965	99,636
Gross Unrealized Gains	87	655
Gross Unrealized Losses	(1,032)	(309)
Available-for-sale debt securities, Fair Value	82,020	99,982
Non-agency Commercial mortgage-backed securities \| Investment grade
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	25,826
Gross Unrealized Gains	226
Gross Unrealized Losses	0
Available-for-sale debt securities, Fair Value	26,052
Non-agency Residential mortgage-backed securities \| Investment grade
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	10,109	9,136
Gross Unrealized Gains	7	3
Gross Unrealized Losses	(185)	(22)
Available-for-sale debt securities, Fair Value	9,931	9,117
Corporate debt securities \| Investment grade
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	11,250	37,585
Gross Unrealized Gains	0	164
Gross Unrealized Losses	(381)	(746)
Available-for-sale debt securities, Fair Value	10,869	37,003
Foreign bonds \| Investment grade
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	489,378	505,396
Gross Unrealized Gains	0	24
Gross Unrealized Losses	(26,330)	(19,012)
Available-for-sale debt securities, Fair Value	463,048	486,408
Asset-backed securities \| Investment grade
Debt Securities, Available-for-sale [Line Items]
Total available-for-sale debt securities, Amortized Cost	12,621
Gross Unrealized Gains	22
Gross Unrealized Losses	0
Available-for-sale debt securities, Fair Value	$ 12,643
Other securities
Debt Securities, Available-for-sale [Line Items]
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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