Available-For-Sale Securities (Investments Classified by Contractual Maturity Date) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 151,585	$ 285,596	$ 203,749
Due in one to five years, Amortized Cost	249,861	172,647	338,130
Due in five to ten years, Amortized Cost	837,926	331,389	344,296
Due after ten years, Amortized Cost	97,046	653,213	652,206
Amortized Cost	1,711,113	1,807,913	2,015,966
Due in one year or less, Fair Value	151,854	285,889	203,942
Due in one to five years, Fair Value	250,483	172,885	338,980
Due in five to ten years, Fair Value	836,598	325,644	330,546
Due after ten years, Fair Value	98,058	637,811	605,352
Available-for-sale securities, at fair value	1,721,030us-gaap_AvailableForSaleSecurities	1,792,078us-gaap_AvailableForSaleSecurities	1,949,697us-gaap_AvailableForSaleSecurities
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	325,978	318,476	427,015
Available-for-sale securities, at fair value	329,591	318,710	417,303
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,717	46,592	50,570
Available-for-sale securities, at fair value	$ 54,446	$ 51,139	$ 53,574

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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