Securities - Schedule of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	$ 2,128,013	$ 4,401,345
Securities Available for Sale, Fair Value	2,208,789	4,496,900
Securities available for sale, Gross Unrealized Gains	80,834	98,561
Securities available for sale, Gross Unrealized Losses	58	3,006
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	150	150
Securities Available for Sale, Fair Value	160	164
Securities available for sale, Gross Unrealized Gains	10	14
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	18,201	248,595
Securities Available for Sale, Fair Value	18,248	249,903
Securities available for sale, Gross Unrealized Gains	47	1,308
Municipal obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	74,967	294,489
Securities Available for Sale, Fair Value	76,132	309,665
Securities available for sale, Gross Unrealized Gains	1,168	15,218
Securities available for sale, Gross Unrealized Losses	3	42
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	1,826,624	2,422,891
Securities Available for Sale, Fair Value	1,904,520	2,480,345
Securities available for sale, Gross Unrealized Gains	77,908	58,150
Securities available for sale, Gross Unrealized Losses	12	696
CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	199,792	1,426,495
Securities Available for Sale, Fair Value	200,696	1,446,076
Securities available for sale, Gross Unrealized Gains	937	21,774
Securities available for sale, Gross Unrealized Losses	33	2,193
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	3,750	4,517
Securities Available for Sale, Fair Value	3,750	4,494
Securities available for sale, Gross Unrealized Gains		11
Securities available for sale, Gross Unrealized Losses		34
Other equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Amortized Cost	4,529	4,208
Securities Available for Sale, Fair Value	5,283	6,253
Securities available for sale, Gross Unrealized Gains	764	2,086
Securities available for sale, Gross Unrealized Losses	$ 10	$ 41

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

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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