Accumulated Other Comprehensive Loss - Changes (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pre-tax Amount
Balance	$ (249,648)	$ (111,823)	$ (159,423)	$ (145,472)
Other comprehensive income (loss)	(30,504)	887	(120,729)	34,536
Balance	(280,152)	(110,936)	(280,152)	(110,936)
Income Tax Benefit (Expense)
Balance	67,238	44,172	63,040	57,461
Other comprehensive income (loss)	8,215	(350)	32,481	(13,639)
Balance	75,453	43,822	75,453	43,822
Net of tax
Balance			2,532,551	2,476,485
Net of Tax	67,388	58,363	204,399	171,998
Other comprehensive (loss) income	(22,289)	537	(88,248)	20,897
Balance	2,423,462	2,581,858	2,423,462	2,581,858
Accumulated other comprehensive loss
Net of tax
Balance	(182,410)	(67,651)	(96,383)	(88,011)
Other comprehensive (loss) income	(22,289)	537	(88,248)	20,897
Balance	(204,699)	(67,114)	(204,699)	(67,114)
Accumulated other comprehensive loss \| Early Adoption \| ASU 2018-02
Income Tax Benefit (Expense)
Early adoption of ASU No. 2018-02			(20,068)
Net of tax
Net of Tax			(20,068)
Investment securities:
Pre-tax Amount
Unrealized net (losses) gains arising during the period	(30,682)	212	(122,070)	33,005
Other comprehensive income (loss)	(30,682)	212	(122,070)	33,005
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	8,262	(84)	32,834	(13,035)
Other comprehensive income (loss)	8,262	(84)	32,834	(13,035)
Net of tax
Balance	(156,373)	(40,116)	(74,117)	(59,958)
Unrealized net gains (losses) arising during the period	(22,420)	128	(89,236)	19,970
Other comprehensive (loss) income	(22,420)	128	(89,236)	19,970
Balance	(178,793)	(39,988)	(178,793)	(39,988)
Investment securities: \| Early Adoption \| ASU 2018-02
Net of tax
Net of Tax			(15,440)
Cash flow derivative hedges:
Pre-tax Amount
Unrealized net (losses) gains arising during the period	178	675	1,341	1,531
Other comprehensive income (loss)	178	675	1,341	1,531
Income Tax Benefit (Expense)
Unrealized net gains (losses) arising during the period	(47)	(266)	(353)	(604)
Other comprehensive income (loss)	(47)	(266)	(353)	(604)
Net of tax
Balance	5,302	2,702	3,680	2,184
Unrealized net gains (losses) arising during the period	131	409	988	927
Other comprehensive (loss) income	131	409	988	927
Balance	$ 5,433	$ 3,111	5,433	$ 3,111
Cash flow derivative hedges: \| Early Adoption \| ASU 2018-02
Net of tax
Net of Tax			$ 765

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