Amortized Cost, Estimated Market Value and Gross Unrealized Appreciation and Depreciation of Available-for-sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	$ 1,769,901
Gross unrealized gains	109,429
Gross unrealized losses	(13,389)
Market value	1,865,941
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	5,091
Gross unrealized gains	107
Gross unrealized losses	(211)
Market value	4,987
Common stock
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	15,111
Gross unrealized gains	1,085
Gross unrealized losses	(2,865)
Market value	13,331
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	45,442
Gross unrealized gains	2,905
Gross unrealized losses	(6)
Market value	48,341
U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	45,341
Gross unrealized gains	964
Gross unrealized losses	0
Market value	46,305
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	251,610
Gross unrealized gains	13,487
Gross unrealized losses	(86)
Market value	265,011
Commercial mortgage backed securities
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	10,057
Gross unrealized gains	152
Gross unrealized losses	0
Market value	10,209
Agency, residential mortgage backed securities
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	312,258
Gross unrealized gains	20,211
Gross unrealized losses	(442)
Market value	332,027
Non-agency, residential mortgage backed securities
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	7,831
Gross unrealized gains	0
Gross unrealized losses	(1,072)
Market value	6,759
Corporate bonds \| Finance
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	729,724
Gross unrealized gains	50,337
Gross unrealized losses	(6,587)
Market value	773,474
Corporate bonds \| Industrial
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	314,663
Gross unrealized gains	17,726
Gross unrealized losses	(2,120)
Market value	330,269
Corporate bonds \| Utilities
Schedule of Available-for-sale Securities [Line Items]
Original or amortized cost	32,773
Gross unrealized gains	2,455
Gross unrealized losses	0
Market value	$ 35,228

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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