INVESTMENT SECURITIES - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 638,386	$ 623,037
Gross Unrealized Gains	7,201	3,666
Gross Unrealized Losses	(4,113)	(1,629)
Estimated Fair Value	641,474	625,074
Fair Value
Less than 12 Months	194,423	169,044
12 Months or More	100,710	199,494
Total	295,133	368,538
Unrealized Losses
Less than 12 Months	(2,275)	(606)
12 Months or More	(1,838)	(1,023)
Total	(4,113)	(1,629)
Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	227,132	145,333
Gross Unrealized Gains	1,111	340
Gross Unrealized Losses	(1,829)	(481)
Estimated Fair Value	226,414	145,192
Fair Value
Less than 12 Months	83,448	43,623
12 Months or More	40,964	54,870
Total	124,412	98,493
Unrealized Losses
Less than 12 Months	(1,038)	(181)
12 Months or More	(791)	(300)
Total	(1,829)	(481)
Commercial MBS and CMOs
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	355,196	353,727
Gross Unrealized Gains	5,993	3,267
Gross Unrealized Losses	(2,246)	(825)
Estimated Fair Value	358,943	356,169
Fair Value
Less than 12 Months	91,732	95,950
12 Months or More	59,746	57,219
Total	151,478	153,169
Unrealized Losses
Less than 12 Months	(1,199)	(339)
12 Months or More	(1,047)	(486)
Total	(2,246)	(825)
Agency bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	56,058	123,977
Gross Unrealized Gains	97	59
Gross Unrealized Losses	(38)	(323)
Estimated Fair Value	56,117	123,713
Fair Value
Less than 12 Months	19,243	29,471
12 Months or More	0	87,405
Total	19,243	116,876
Unrealized Losses
Less than 12 Months	(38)	(86)
12 Months or More	0	(237)
Total	$ (38)	$ (323)