FAIR VALUES OF FINANCIAL INSTRUMENTS: (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value measurement
Securities available-for-sale	$ 926,717	$ 784,916
U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	103,633	25,364
Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	243,382	178,743
Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	22,104
Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	281,311	343,616
State and municipal obligations
Fair value measurement
Securities available-for-sale	264,434	233,935
Collateralized debt obligations
Fair value measurement
Securities available-for-sale	3,619	3,258
Level 1
Fair value measurement
Securities available-for-sale	0	0
Level 2
Fair value measurement
Securities available-for-sale	920,533	778,523
Derivative Assets	828	218
Derivative Liabilities	(828)	(218)
Level 2 | U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	103,633	25,364
Level 2 | Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	243,382	178,743
Level 2 | Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	22,104
Level 2 | Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	281,311	343,616
Level 2 | State and municipal obligations
Fair value measurement
Securities available-for-sale	261,869	230,800
Level 3
Fair value measurement
Securities available-for-sale	6,184	6,393
Level 3 | State and municipal obligations
Fair value measurement
Securities available-for-sale	2,565	3,135
Level 3 | Collateralized debt obligations
Fair value measurement
Securities available-for-sale	$ 3,619	$ 3,258