Securities - Amortized Cost and Fair Value of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	$ 1,986,882	$ 4,401,345
Securities available for sale, Gross Unrealized Gains	61,599	98,561
Securities available for sale, Gross Unrealized Losses	39	3,006
Securities Available for Sale, Fair Value	2,048,442	4,496,900
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	150	150
Securities available for sale, Gross Unrealized Gains	8	14
Securities Available for Sale, Fair Value	158	164
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	18,096	248,595
Securities available for sale, Gross Unrealized Gains	11	1,308
Securities Available for Sale, Fair Value	18,107	249,903
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	49,608	294,489
Securities available for sale, Gross Unrealized Gains	571	15,218
Securities available for sale, Gross Unrealized Losses	14	42
Securities Available for Sale, Fair Value	50,165	309,665
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	1,715,524	2,422,891
Securities available for sale, Gross Unrealized Gains	58,903	58,150
Securities available for sale, Gross Unrealized Losses	21	696
Securities Available for Sale, Fair Value	1,774,406	2,480,345
CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	196,723	1,426,495
Securities available for sale, Gross Unrealized Gains	1,354	21,774
Securities available for sale, Gross Unrealized Losses		2,193
Securities Available for Sale, Fair Value	198,077	1,446,076
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	2,250	4,517
Securities available for sale, Gross Unrealized Gains		11
Securities available for sale, Gross Unrealized Losses		34
Securities Available for Sale, Fair Value	2,250	4,494
Other equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale, amortized cost	4,531	4,208
Securities available for sale, Gross Unrealized Gains	752	2,086
Securities available for sale, Gross Unrealized Losses	4	41
Securities Available for Sale, Fair Value	$ 5,279	$ 6,253

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

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

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.

+ References+ Details

- 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.

+ References+ Details