FAIR VALUE MEASUREMENTS (Details) (Measured on a Recurring Basis:, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Total
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	$ 1,357,211
Total | Government agency and government-sponsored enterprices residential mortgage-backed securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,036,856
Total | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	45,887
Total | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	247,280
Total | Corporate securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	17,255
Total | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	9,933
Level 1
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	8,159
Level 1 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	8,159
Level 2
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,303,165
Level 2 | Government agency and government-sponsored enterprices residential mortgage-backed securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,036,856
Level 2 | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	247,280
Level 2 | Corporate securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	17,255
Level 2 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,774
Level 3
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	45,887
Level 3 | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	$ 45,887