EARNINGS PER SHARE: Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Basic EPS computation:
Numerator-net income (in dollars)	$ 3,009		$ 1,520		$ 3,059		$ 2,654		$ 2,034		$ 1,993		$ 1,680		$ 1,697		$ 10,242	$ 7,404	$ 6,358
Denominator-weighted average common shares outstanding																	22,531,480	22,478,306	22,450,252
Basic EPS (in dollars per share)	$ 0.13	[1]	$ 0.07	[1]	$ 0.14	[1]	$ 0.12	[1]	$ 0.09	[1]	$ 0.09	[1]	$ 0.07	[1]	$ 0.08	[1]	$ 0.45	$ 0.33	$ 0.28
Diluted EPS computation:
Numerator-net income (in dollars)	$ 3,009		$ 1,520		$ 3,059		$ 2,654		$ 2,034		$ 1,993		$ 1,680		$ 1,697		$ 10,242	$ 7,404	$ 6,358
Denominator-weighted average common shares outstanding																	22,531,480	22,478,306	22,450,252
Effect of dilutive stock options																	92,000	70,000	44,000
Weighted average common shares and common stock equivalents																	22,618,330	22,548,340	22,494,151
Diluted (in dollars per share)	$ 0.13	[1]	$ 0.07	[1]	$ 0.14	[1]	$ 0.12	[1]	$ 0.09	[1]	$ 0.09	[1]	$ 0.07	[1]	$ 0.08	[1]	$ 0.45	$ 0.33	$ 0.28

[1] Quarterly earnings per share may vary from annual earnings per share due to rounding.