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Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Held-to-maturity securities
Amortized Cost	$ 2,400	$ 2,400
Estimated Fair Value	2,400	2,400
Carrying Value	2,400	2,400
Available-for-sale securities
Amortized Cost	5,209,023	5,372,594
Gross Unrealized Gains	76,469	65,104
Gross Unrealized Losses	(60,449)	(133,119)
Total investment securities	5,225,043	5,304,579
Estimate Of Fair Value Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	5,225,043	5,304,579
Carrying Reported Amount Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	5,225,043	5,304,579
Other Debt Securities [Member]
Held-to-maturity securities
Amortized Cost	2,400	2,400
Estimated Fair Value	2,400	2,400
Carrying Value	2,400	2,400
Mortgage Backed Securities [Member]
Available-for-sale securities
Amortized Cost	4,923,587	5,096,165
Gross Unrealized Gains	58,667	56,110
Gross Unrealized Losses	(54,391)	(124,574)
Mortgage Backed Securities [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	4,927,863	5,027,701
Mortgage Backed Securities [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	4,927,863	5,027,701
U S Government Corporations And Agencies Securities [Member]
Available-for-sale securities
Total investment securities	1,646,495	1,799,807
Mortgage Backed Securities Issued By U S Government Sponsored Enterprises [Member]
Available-for-sale securities
Total investment securities	3,255,372	3,200,042
Mortgage Backed Securities Issued By Private Enterprises [Member]
Available-for-sale securities
Total investment securities	25,996	27,852
U S States And Political Subdivisions [Member]
Available-for-sale securities
Amortized Cost	257,361	248,354
Gross Unrealized Gains	16,550	8,063
Gross Unrealized Losses	(5,817)	(8,007)
U S States And Political Subdivisions [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	268,094	248,410
U S States And Political Subdivisions [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	268,094	248,410
Equity Securities [Member]
Available-for-sale securities
Amortized Cost	28,075	28,075
Gross Unrealized Gains	1,252	931
Gross Unrealized Losses	(241)	(538)
Equity Securities [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	29,086	28,468
Equity Securities [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Available-for-sale securities
Total investment securities	$ 29,086	$ 28,468

X

- Definition

Amount of accumulated unrealized gain before deducting unrealized loss on investments in available-for-sale securities impacting investments.

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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 after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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