INVESTMENTS - Summary of Held-To-Maturity and Available-For-Sale Investment Securities (Detail) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	$ 2,724	$ 17,406
Held-to-Maturity Unrealized Gains	229	678
Held-to-Maturity Unrealized Losses	0	(18)
Held-to-Maturity Market Value	2,953	18,066
Available-for-Sale Amortized Cost	1,092,648	904,546
Available-for-Sale Unrealized Gains	28,049	17,291
Available-for-Sale Unrealized Losses	(518)	(2,727)
Available-for-Sale Market Value	1,120,179	919,110
U.S. Treasuries
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost		13,959
Held-to-Maturity Unrealized Gains		390
Held-to-Maturity Unrealized Losses		(18)
Held-to-Maturity Market Value		14,331
Available-for-Sale Amortized Cost		0
Available-for-Sale Unrealized Gains		0
Available-for-Sale Unrealized Losses		0
Available-for-Sale Market Value		0
Securities of U.S. government agencies and corporations
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	0	0
Held-to-Maturity Unrealized Gains	0	0
Held-to-Maturity Unrealized Losses	0	0
Held-to-Maturity Market Value	0	0
Available-for-Sale Amortized Cost	5,027	105,028
Available-for-Sale Unrealized Gains	85	957
Available-for-Sale Unrealized Losses	0	0
Available-for-Sale Market Value	5,112	105,985
Mortgage-backed securities
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	95	118
Held-to-Maturity Unrealized Gains	3	4
Held-to-Maturity Unrealized Losses	0	0
Held-to-Maturity Market Value	98	122
Available-for-Sale Amortized Cost	1,065,948	775,867
Available-for-Sale Unrealized Gains	27,503	15,513
Available-for-Sale Unrealized Losses	(267)	(2,630)
Available-for-Sale Market Value	1,093,184	788,750
Obligations of state and other political subdivisions
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	2,629	3,329
Held-to-Maturity Unrealized Gains	226	284
Held-to-Maturity Unrealized Losses	0	0
Held-to-Maturity Market Value	2,855	3,613
Available-for-Sale Amortized Cost	11,509	13,708
Available-for-Sale Unrealized Gains	154	207
Available-for-Sale Unrealized Losses	(26)	(91)
Available-for-Sale Market Value	11,637	13,824
Other securities
Investment Holdings [Line Items]
Held-to-Maturity Amortized Cost	0	0
Held-to-Maturity Unrealized Gains	0	0
Held-to-Maturity Unrealized Losses	0	0
Held-to-Maturity Market Value	0	0
Available-for-Sale Amortized Cost	10,164	9,943
Available-for-Sale Unrealized Gains	307	614
Available-for-Sale Unrealized Losses	(225)	(6)
Available-for-Sale Market Value	$ 10,246	$ 10,551

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

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