INVESTMENT SECURITIES (Amortized Cost and Estimated Fair Value of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
INVESTMENT SECURITIES
Equity securities, at fair value	$ 1,435	$ 1,351
Available for Sale, Amortized Cost
Due in one year or less	21,146
Due after one year through five years	28,707
Due after five years through ten years	93,484
Due after ten years	110,583
Total	1,213,382
Available for Sale, Estimated Fair Value
Due in one year or less	21,381
Due after one year through five years	29,691
Due after five years through ten years	93,093
Due after ten years	109,524
Available-for-sale debt securities, at fair value	1,216,341	1,182,609
Equity securities
INVESTMENT SECURITIES
Equity securities, at amortized cost	1,096	1,068
Equity securities, at fair value	1,435	1,351
Residential - U.S. Government-sponsored entities
Available for Sale, Amortized Cost
Mortgage-backed securities	814,051
Available for Sale, Estimated Fair Value
Mortgage-backed securities	815,266
Available-for-sale debt securities, at fair value	815,266	778,826
Commercial - U.S. Government agencies and sponsored entities
Available for Sale, Amortized Cost
Mortgage-backed securities	85,778
Available for Sale, Estimated Fair Value
Mortgage-backed securities	85,879
Available-for-sale debt securities, at fair value	85,879	87,469
Residential - Non-government agencies
Available for Sale, Amortized Cost
Mortgage-backed securities	18,318
Available for Sale, Estimated Fair Value
Mortgage-backed securities	18,800
Available-for-sale debt securities, at fair value	18,800	23,423
Commercial - Non-government agencies
Available for Sale, Amortized Cost
Mortgage-backed securities	41,315
Available for Sale, Estimated Fair Value
Mortgage-backed securities	42,707
Available-for-sale debt securities, at fair value	$ 42,707	$ 42,972