FAIR VALUE MEASUREMENTS (Details) (Measured on a Recurring Basis:, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	$ 1,355,385	$ 1,326,358
Total | Government agency and government-sponsored enterprises residential mortgage-backed securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	909,536	1,124,534
Total | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	44,684	45,149
Total | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	348,041	126,797
Total | Corporate debt securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	42,365	25,128
Total | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	10,759	4,750
Level 1
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	8,985	2,976
Level 1 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	8,985	2,976
Level 2
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,301,716	1,278,233
Level 2 | Government agency and government-sponsored enterprises residential mortgage-backed securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	909,536	1,124,534
Level 2 | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	348,041	126,797
Level 2 | Corporate debt securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	42,365	25,128
Level 2 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,774	1,774
Level 3
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	44,684	45,149
Level 3 | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	$ 44,684	$ 45,419