FAIR VALUE MEASUREMENTS (Details) (Measured on a Recurring Basis:, USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Liabilities at fair value	$ 0
Transfers of assets
Amounts transferred from Level 1 to Level 2	0
Amounts transferred from Level 2 to Level 1	0
Amounts transferred in Level 3	0
Amounts transferred out of Level 3	0
Total
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,473,578
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	887,737
Total | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	40,917
Total | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	424,174
Total | Corporate securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	83,132
Total | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	37,618
Level 1
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	516
Level 1 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	516
Level 2
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	1,432,145
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	887,737
Level 2 | Municipal securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	424,174
Level 2 | Corporate securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	83,132
Level 2 | Other securities
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	37,102
Level 3
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	40,917
Level 3 | Covered private label CMOs
Assets measured and recorded at fair value on a recurring and nonrecurring basis
Assets at fair value	$ 40,917