Securities (Securities available for sale) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,342,977	$ 2,248,181
Equity securities with a readily determinable fair value	16,916
Total	2,342,977
Gross Unrealized Gains	1,580
Gross Unrealized Losses	(70,342)
Estimated Fair Value	2,274,215	2,216,753
Estimated Fair Value	2,274,215
Amortized Cost		2,248,181
Gross Unrealized Gains		10,911
Gross Unrealized Losses		(42,339)
Securities available for sale		2,216,753
Total debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,326,061
Gross Unrealized Gains	1,580
Gross Unrealized Losses	(70,342)
Estimated Fair Value	2,257,299
Amortized Cost		2,231,885
Gross Unrealized Gains		10,533
Gross Unrealized Losses		(42,339)
Securities available for sale		2,200,079
U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27,112
Gross Unrealized Gains	0
Gross Unrealized Losses	(115)
Estimated Fair Value	26,997
Amortized Cost		5,358
Gross Unrealized Gains		8
Gross Unrealized Losses		(38)
Securities available for sale		5,328
Mortgage and asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,926,803
Gross Unrealized Gains	1,341
Gross Unrealized Losses	(56,325)
Estimated Fair Value	1,871,819
Amortized Cost		1,785,467
Gross Unrealized Gains		5,856
Gross Unrealized Losses		(37,587)
Securities available for sale		1,753,736
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	372,146
Gross Unrealized Gains	239
Gross Unrealized Losses	(13,902)
Estimated Fair Value	$ 358,483
Amortized Cost		441,060
Gross Unrealized Gains		4,669
Gross Unrealized Losses		(4,714)
Securities available for sale		441,015
Equity securities with a readily determinable fair value
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		16,296
Gross Unrealized Gains		378
Gross Unrealized Losses		0
Securities available for sale		$ 16,674

Marketable Securities, Amortized Cost Basis

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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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of 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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Amount of investment in marketable security.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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