INVESTMENTS - Age of Gross Unrealized Losses and Associated Fair Value by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	$ 268,775	$ 353,016
Less than 12 Months Unrealized Loss	(1,891)	(2,024)
12 Months or More Fair Value	4,913	31,857
12 Months or More Unrealized Loss	(62)	(98)
Total Fair Value	273,688	384,873
Total Unrealized Loss	(1,953)	(2,122)
Mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	264,090	343,883
Less than 12 Months Unrealized Loss	(1,740)	(1,938)
12 Months or More Fair Value	4,896	29,562
12 Months or More Unrealized Loss	(62)	(93)
Total Fair Value	268,986	373,445
Total Unrealized Loss	(1,802)	(2,031)
Obligations of state and other political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	0	0
Less than 12 Months Unrealized Loss	0	0
12 Months or More Fair Value	0	2,278
12 Months or More Unrealized Loss	0	(5)
Total Fair Value	0	2,278
Total Unrealized Loss	0	(5)
Other securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 Months Fair Value	4,685	9,133
Less than 12 Months Unrealized Loss	(151)	(86)
12 Months or More Fair Value	17	17
12 Months or More Unrealized Loss	0	0
Total Fair Value	4,702	9,150
Total Unrealized Loss	$ (151)	$ (86)