FAIR VALUES OF FINANCIAL INSTRUMENTS: (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair value measurement
Securities available-for-sale	$ 897,053	$ 914,560
U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	1,467	1,633
Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	187,936	197,764
Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	17	4,391
Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	484,655	506,741
State and municipal obligations
Fair value measurement
Securities available-for-sale	207,675	194,987
Collateralized debt obligations
Fair value measurement
Securities available-for-sale	15,303	9,044
Level 1
Fair value measurement
Securities available-for-sale	0	0
Level 2
Fair value measurement
Securities available-for-sale	875,850	900,991
Derivative Assets	1,062	1,195
Derivative Liabilities	(1,062)	(1,195)
Level 2 | U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	1,467	1,633
Level 2 | Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	187,936	197,764
Level 2 | Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	17	4,391
Level 2 | Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	484,655	506,741
Level 2 | State and municipal obligations
Fair value measurement
Securities available-for-sale	201,775	190,462
Level 3
Fair value measurement
Securities available-for-sale	21,203	13,569
Level 3 | State and municipal obligations
Fair value measurement
Securities available-for-sale	5,900	4,525
Level 3 | Collateralized debt obligations
Fair value measurement
Securities available-for-sale	$ 15,303	$ 9,044