MARKETABLE SECURITIES - Securities in Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Gross Unrealized Losses
Less Than 12 Months	$ (3,478)	$ (1,799)
12 Months or Longer	(4,508)	(1,747)
Total	(7,986)	(3,546)
Estimated Fair Value
Less Than 12 Months	127,003	144,484
12 Months or Longer	106,348	76,601
Total	233,351	221,085
Gross Unrealized Losses
Less Than 12 Months	(1,145)	(94)
12 Months or Longer	(843)	(354)
Total	(1,988)	(448)
Estimated Fair Value
Less Than 12 Months	77,942	15,729
12 Months or Longer	28,004	29,708
Total	105,946	45,437
Corporate bonds
Gross Unrealized Losses
Less Than 12 Months	(643)	(50)
12 Months or Longer	0	0
Total	(643)	(50)
Estimated Fair Value
Less Than 12 Months	18,141	8,019
12 Months or Longer	0	0
Total	18,141	8,019
Municipal securities
Gross Unrealized Losses
Less Than 12 Months	(17)	0
12 Months or Longer	(288)	(200)
Total	(305)	(200)
Estimated Fair Value
Less Than 12 Months	807	0
12 Months or Longer	7,410	7,546
Total	8,217	7,546
Mortgage-backed securities
Gross Unrealized Losses
Less Than 12 Months	(314)	(658)
12 Months or Longer	(3,506)	(1,135)
Total	(3,820)	(1,793)
Estimated Fair Value
Less Than 12 Months	16,151	42,881
12 Months or Longer	75,091	47,797
Total	91,242	90,678
Collateralized mortgage obligations
Gross Unrealized Losses
Less Than 12 Months	(2,504)	(1,091)
12 Months or Longer	(714)	(412)
Total	(3,218)	(1,503)
Estimated Fair Value
Less Than 12 Months	91,904	93,584
12 Months or Longer	23,847	21,258
Total	115,751	114,842
Municipal securities
Gross Unrealized Losses
Less Than 12 Months	(952)	(37)
12 Months or Longer	(529)	(181)
Total	(1,481)	(218)
Estimated Fair Value
Less Than 12 Months	68,662	9,230
12 Months or Longer	19,466	19,961
Total	88,128	29,191
Mortgage-backed securities
Gross Unrealized Losses
Less Than 12 Months	(158)	(57)
12 Months or Longer	(314)	(173)
Total	(472)	(230)
Estimated Fair Value
Less Than 12 Months	6,686	6,499
12 Months or Longer	8,538	9,747
Total	15,224	16,246
Collateralized mortgage obligations
Gross Unrealized Losses
Less Than 12 Months	(35)	0
12 Months or Longer	0	0
Total	(35)	0
Estimated Fair Value
Less Than 12 Months	2,594	0
12 Months or Longer	0	0
Total	$ 2,594	$ 0