Investment Securities (Amortization Cost, Gross Unrealized Gains/Losses, and Fair Value) (Details 1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 1,864,456	$ 2,022,158
Available-for-Sale: Gross Unrealized Gains	12,140	9,225
Available-for-Sale: Gross Unrealized Losses	(17,340)	(23,441)
Available-for-Sale	1,859,256	2,007,942
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	3,668,811	3,482,092
Held-to-Maturity: Gross Unrealized Gains	19,655	11,959
Held-to-Maturity: Gross Unrealized Losses	(50,970)	(80,057)
Held-to-Maturity: Fair Value	3,637,496	3,413,994
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	189	56
Available-for-Sale: Gross Unrealized Gains	1	0
Available-for-Sale: Gross Unrealized Losses	0	0
Available-for-Sale	190	56
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	396,578	189,645
Available-for-Sale: Gross Unrealized Gains	3,582	1,726
Available-for-Sale: Gross Unrealized Losses	(1,196)	(929)
Available-for-Sale	398,964	190,442
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	1,803,146	1,861,874
Held-to-Maturity: Gross Unrealized Gains	6,771	3,886
Held-to-Maturity: Gross Unrealized Losses	(32,071)	(51,773)
Held-to-Maturity: Fair Value	1,777,846	1,813,987
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	560,506	589,311
Available-for-Sale: Gross Unrealized Gains	3,328	1,779
Available-for-Sale: Gross Unrealized Losses	(8,591)	(12,563)
Available-for-Sale	555,243	578,527
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	1,010,892	758,835
Held-to-Maturity: Gross Unrealized Gains	4,599	1,590
Held-to-Maturity: Gross Unrealized Losses	(11,013)	(20,259)
Held-to-Maturity: Fair Value	1,004,478	740,166
Commercial - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	143,396	63,864
Available-for-Sale: Gross Unrealized Gains	982	0
Available-for-Sale: Gross Unrealized Losses	(3,953)	(4,484)
Available-for-Sale	140,425	59,380
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	174,473	176,393
Held-to-Maturity: Gross Unrealized Gains	336	147
Held-to-Maturity: Gross Unrealized Losses	(5,977)	(5,177)
Held-to-Maturity: Fair Value	168,832	171,363
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,100,480	842,820
Available-for-Sale: Gross Unrealized Gains	7,892	3,505
Available-for-Sale: Gross Unrealized Losses	(13,740)	(17,976)
Available-for-Sale	1,094,632	828,349
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	2,988,511	2,797,102
Held-to-Maturity: Gross Unrealized Gains	11,706	5,623
Held-to-Maturity: Gross Unrealized Losses	(49,061)	(77,209)
Held-to-Maturity: Fair Value	2,951,156	2,725,516
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	365,787	394,485
Available-for-Sale: Gross Unrealized Gains	450	493
Available-for-Sale: Gross Unrealized Losses	(2,515)	(2,577)
Available-for-Sale	363,722	392,401
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	353,298	353,122
Held-to-Maturity: Gross Unrealized Gains	645	186
Held-to-Maturity: Gross Unrealized Losses	(603)	(1,093)
Held-to-Maturity: Fair Value	353,340	352,215
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	173,002	559,800
Available-for-Sale: Gross Unrealized Gains	3,738	5,227
Available-for-Sale: Gross Unrealized Losses	(11)	(1,031)
Available-for-Sale	176,729	563,996
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	233,609	234,602
Held-to-Maturity: Gross Unrealized Gains	7,287	6,150
Held-to-Maturity: Gross Unrealized Losses	0	0
Held-to-Maturity: Fair Value	240,896	240,752
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	224,998	224,997
Available-for-Sale: Gross Unrealized Gains	59	0
Available-for-Sale: Gross Unrealized Losses	(1,074)	(1,857)
Available-for-Sale	223,983	223,140
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	93,393	97,266
Held-to-Maturity: Gross Unrealized Gains	17	0
Held-to-Maturity: Gross Unrealized Losses	(1,306)	(1,755)
Held-to-Maturity: Fair Value	$ 92,104	$ 95,511

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 amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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