INCOME TAXES: (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income taxes computed at the statutory rate	$ 17,414	$ 20,403	$ 14,206
Add (deduct) tax effect of:
Tax exempt income	(4,102)	(3,992)	(4,047)
THFF FSI non-deductable goodwill	0	1,797	0
ESOP dividend deduction	(102)	(47)	(164)
State tax, net of federal benefit	1,483	1,978	829
Affordable housing credits	(148)	(148)	(148)
Federal tax reform	6,282
Other, net	(205)	(108)	(284)
TOTAL	$ 20,622	$ 19,883	$ 10,392